Most 32 bit software runs fine with 64 bit 7, unless you're installing a game that was built for 32/64 bit Xp, sometimes that doesn't work with 7. The real issue are 32 bit drivers in 64 bit 7, that is a pickle!
I have a 32 bit printer that should work with 64 bit Windows 7 since it was compatible with 64 bit vista, but Microsoft says the printer doesn't fly with 64 bit 7 but Dell doesn't have anything updated for that printer up to vista. I ended up having to install a 32 bit virtual machine just to use it.
I'd so go for 64 bit Windows since it feels more smoother performance wise. Installer packages decompress and install much faster, boot times are slightly faster, and it's actually a little more secure than 32 bit. Also, after Windows 8 comes out next year, it basically marks the end of the 32 bit computing era...