I do not know if this applies to the other versions of the Office Suite 2007 set.
I do not know if this applies to the full version of Outlook.

But when I installed the Microsoft Office Home and Student 2007, it changed my spell check in Outlook Express to FRENCH, and will not allow me to choose any other language.

So far the only known solution is to BUY Proofing Tools for Microsoft 2003, according to the nice man I am sure was sitting in an office in India, safely outside the continental United State.

This is, by the way, a known bug and they are working on a solution.  He thinks.

Microsoft Office Home and Student 2007 does have a spellcheck in English, so I have no idea why it changed Outlook Express, which was not downloaded with it.

But trying to solve the problem has wasted two hours of my life that I'll never get back.

Thank you, Bill Gates.

What a mystery!!
Are you running it on Windows XP?
If so, go into Control Panel, and check in "Regional / Language" options - maybe French is selected somewhere.

I had to change my language in there once to display dates properly
in Office the Australian way!!

That' the problem...when I go to Regional/Language options, the only option available to me is French.  I can't make any other language choice.

I am told by Manju, the Microsoft techician, that this is a known bug and a patch will be released soon.

At first they insisted I had a Canadian version of XP, but I don't think so.

When I go into "R&L Options" there are two tabs:  "Regional Options" and "Languages".

Try  this when Office and Outlook are closed.
Click on "Languages" Tab.
Then click the "Details" button.
Then click the "ADD" button.  [ The "Settings" tab ].
Then click the upside-down-^ under "Input languages" and a pick list of languages should display.  Choose your language and click OK.
You should be back at the "Settings" Tab.
Choose your language in the "Default input language" in the upper half of the window.
Click OK.
Click Apply.
Click OK.
Reboot Windows XP.

It's not that I didn't do all that. English is the default that is shown for XP and Office.  I don't have any prolems with the spell check or the options selected for them--everything is in English. I rebooted just to make sure.

But when  I go back to Outlook Express, it only offers me French asa language. It won't let me add English. It doesn't offer a pick list (well, it does, but the list only has France).

It's really a funky thing.

A known bug. 

But an irritating one.

I GUESS THE BUG WINS for now.
Outlook Ex pressHelp says that spell checking uses Office Dictionaries only, so now we know why it happened.  I looked up my OFFICE 2003 HELP and found the item:CHECK_THE_SPELLING_AND_GRAMMAR_OF_TEXT_IN_ANOTHER_LANGUAGE
This is what it says [ Maybe OFFICE2007Help has a better answer]:
Some of the content in this topic may not be applicable to some languages.
The feature described in this Help topic is only available if support for the language you want to use is enabled through Microsoft Office Language Settings.
1.    Install the spelling and grammar tools for the language you want.
If you check spelling or grammar in another language, and the correct files aren't available on your computer, then Microsoft Word will try to automatically install them. If Word can't install the correct files, you may need to obtain Microsoft Office 2003 Proofing Tools.
2.    Turn on automatic language detection.
 How?
If you're working in more than one language within a document, Microsoft Word can automatically detect each language as you type it.
1.    On the Tools menu, point to Language, and then click Set Language.
2.    Select the Detect language automatically check box.
Notes
o    To turn off automatic language detection in your document, clear the Detect language automatically check box.
o    To turn off the automatic detection of a particular language, remove it from the list of enabled languages in the Microsoft Office Language Settings tool. Remove the language only if you don't want to use features particular to that language (for example, date formats) in Word and other Microsoft Office programs.
3.    Set spelling and grammar options for the language you want to work in.
 How?
0.    On the Tools menu, click Options, and then click the Spelling & Grammar tab.
1.    Set the options you want.
4.    Check spelling or grammar as usual.
 How?
By default, Microsoft Word checks spelling and grammar automatically as you type, using wavy red underlines to indicate possible spelling problems and wavy green underlines to indicate possible grammatical problems.
You can also check spelling and grammar all at once.
 Check spelling and grammar automatically as you type
0.    Make sure automatic spelling and grammar checking are turned on.
 How?
1.    On the Tools menu, click Options, and then click the Spelling & Grammar tab.
2.    Select the Check spelling as you type and Check grammar as you type check boxes.
1.    Type in the document.
2.    Right-click a word with a wavy red or green underline, and then select the command or the spelling alternative you want.
 Tips
o    You can use AutoCorrect to automatically correct spelling as you type, without having to confirm each correction. For example, if you type definately and then type a space or other punctuation, AutoCorrect automatically replaces it with "definitely."
o    If Word finds a lowercase word, for example "london," that is listed in the main dictionary with a different capitalization ("London"), the capitalization may be flagged or corrected automatically as you type. To prevent this, add the lowercase form of the word to a custom dictionary.
 Check spelling and grammar all at once
This method is useful if you want to postpone proofing a document until after you finish editing it. You can check for possible spelling and grammatical problems, and then confirm each correction.
Note   By default, Word checks both spelling and grammar. If you want to check spelling only, click Options on the Tools menu, click the Spelling & Grammar tab, clear the Check grammar with spelling check box, and then click OK.
5.    On the Standard toolbar, click Spelling and Grammar  .
6.    When Word finds a possible spelling or grammatical problem, make your changes in the Spelling and Grammar dialog box.
 Tips
o    You can correct spelling and grammar directly in the document while the Spelling and Grammar dialog box is still displayed. Type your correction in the document, and then click Resume in the Spelling and Grammar dialog box.
o    For a detailed explanation of a grammar flag, right-click the flag, click Grammar, and then click Explain in the Grammar dialog box.
Note  If you mistype a word but the result is not a misspelling (for example, typing "from" instead of "form" or "there" instead of "their"), the spelling checker will not flag the word. To catch those types of problems, use the grammar checker.

Attached Link: http://www.snapfiles.com/get/spelloe.html

This solution came from the Microsoft Support Center so I guess it is the official fix, such as it is.