New PC not extracting files correctly.

Hi,

I am creating a new PC, the specs are (roughly)
A8N-E board w/ AMD 64 6800+
512mb (x2) PC3200 Dual Channel
eVGA GeForce 7800GT 256mb
80 GB Western Digital SATA 8mb

I'm having the strangest issue, where some software packages (including GalCivII) won't extract, citing an error in the CRC table or an incomplete download (neither of which are the case).

I can install some things okay, I had no problem installing this:

Nero
PowerDVD
Stardock Central
WinZIP9

But I am getting errors with Install Shield when I try these installs

FEAR demo
3dMark2006

And Stardock seems to extrac and install the same files over and over again. Any ideas what might be causing this!?

Thanks,
Scott

PS: I did install the 1.2.2.2 update from AMD.