I am NOT advocating piracy here, not do I have intentions of releasing modified apps as my own. I am just curious how things work. I will be Jailbreaking my (5.01) Ipad 2 3G 64 Gig AT&T model, when an untethered Jailbreak is available. I have a Windows 7 64 bit pc.

Is it possible to decompress *.ipa files. If so, are they compiled like Windows executables, or will I be able to look at source code. I would like to play around by changing some values, then loading and trying to run the modified apps. This will help me with some development aspirations that I have.

Thanks

You will not be able to view source code.

Ipa files are just zip files, either open using a zip or rar program, but you won't find much in there

You won't be able to achieve what you want by simply looking inside the IPA files I'm afraid. If you really do have development aspirations on the iPad, modifying other folks iPad apps is probably not the way to start.
Strictly speaking, neither is using a Windows platform (if you have no IOS development grounding at all), but it can be done. I suggest you get yourself a good book on Objective-C, or look at some of the many free courses in the iTunes University on developing IOS apps and take it from there.