Nvidia Drivers

[Team17_999]

Hi all, i recently had a gaming computer assembled for me and installed windows etc. I downloaded the latest driver for my card and when i install it it says that the file cannot be unpacked and it's corrupted and that i need to verify it's integrity. Ive downloaded it from nvidia about 6 times with the same message. I used the xfx cd and downloaded the latest driver from xfx site and the same message comes. Now ive noticed that nearly everything i get from the internet is getting a corrupted file message, and i cant install the program.
Examples. Avira anti virus, about 3 corrupt files (can see approx how many are corrupt when it extracts).
avg anti virus, at the end of downloading the files to install it, it said some files are missing, please reinstall etc etc. It's even giving me corrupted errors when i install a game from a disc, which i know works fine since i installed it on my brothers computer before i tried it on mine (different file is corrupt each time i do a reinstall).
I wiped the comp clean and reinstalled vista about 3-4hours ago and the same message is coming. I dont think its a virus because i have several install files stored on a portable hdd and adobe/avira/vlc are giving me corrupted messages.
Also, i keep getting messages where system proccess keep getting shutdown like rundll, superfetch, windows modules installer etc
Firefox keeps crashing/Internet is going really slow
I dont want you solve all these problems, just giving as much info as i can which will let me install files without it getting corrupted

Specs:
Gigabyte ep43t-ud3l
Intel Core 2 quad Q8400 @ 2.66ghz
500 gb hdd
4gb ram (2gbx2)
Nvidia 275 gtx
LG super multi disc writer
Windows Vista home premium 32 bit
600 watt psu

 

[Mousemonkey]

Check your RAM voltage, I've had installs go a bit weird because the RAM voltage was slightly off, 1.9v should be safe. Complete shot in the dark but you never know.