When I installed, there were two line, one for 32 bit, one for 64 (the 64 bit one was selected by default) I clicked on the 32 bit line to install the 32 bit version and on the 64 one for the 64 bit version.

In fact, since an image is worth a thousand words (especially because I'm French, and my English isn't always as good as I wish it would be :) )

http://img259.imageshack.us/my.php?image=installms3.jpg

So, that's the first dialog I see when installing, and by clicking on one of the two lines, I'm able to choose what version I want to install.
So, by launching the install twice I can install both version without problem :)

Ab

Lol, I went through hell to try and post an image, seems I'm not gifted so you will need to copy paste the link :) (No nudity ;) )