Corupt Install files?

[bindo]

Hey
I've just built my own PC, installed windows and everything. The only problem i'm having is that most of the programs i'm downloading won't install...it comes up with an error message along the lines of "install file corrupt", "not enough system memory or corrupted file".
It's a brand new PC with one gig of ram and a 200 gig hard drive...it's getting really annoying now. Any ideas how i can solve this?
Thank you!!

[fredered]

if you have one it may be worth disabling your virus checker, as young as you know for sure the file is safe, as once i had a problem with macafee corrupting files so they wouldnt download