I have bought and downloaded three games from this site yet when I go to install them, they never get pass the integrity check and it just says that they are corrupt. I'm using Vista so im sure that doesn't help. I have also downloaded them manually and with the downloader yet so far nothing has worked.

try pausing the download in the downloader, when trying to download. pause it a couple times through and that should make sure they aren't corrupt

Ive tried that, paused it like 2-3 times but it still wont work

That's odd, it usually works for me, have you emailed support@gog.com?

no but no worries now, i figured out the problem, i had spybot running and didnt realized it, thanks for the help though

I was having the same problem, so I thought I would share my fix. I had one marginally bad RAM stick in my computer. I used the memory tester on an Ubuntu install disk and found that just two particular locations on one of my sticks was bad. For me it was a big tip-off when I could download the file on a different computer and have it work. Copying it to this computer from the working one led to a corrupt installer.
The weirdness was that manually computing the MD5 of the installer gave a different fingerprint each time I did it.