Quote - I never put the PC to sleep if you mean the energy saving option. I thought the hibernation is used for notebooks only (for low leveled battery power?). But Windows does the page filing for these modes anyway, even though I did turn the sleeping mode off and I'm not on a Notebook? If I understand you correctly the only thing I have to do is to change the page file size in Win7? Where is the option hidden? I will give it a try on my other HDD.

Have a look at this page and try it if you want:
www.windows7hacker.com/index.php/2009/05/what-is-hiberfilsys-and-how-to-delete-in-windows-7-free-up-hard-drive-space/

NOTE that I'm not recommending it or anything like that, although it's probably safe. I haven't tried it because I do like to put my PCs into hibernation, and removing the hiberfil.sys file will remove your ability to do that.

As Magic_Man posted above, it's better not to mess with your page file size, but that's under the advanced options in  My Computer>Properties.
You can also type F1 to get to the Windows Help and put "page file" in the search, then click on the "Change the size of virtual memory" link. Unless you really know what you're doing, that's not a particularly good idea.