cant install latest drivers, get "cannot be unpacked" message

Hi All,

I am trying to update the nvidia graphics driver and the nvidia nForce
chipset drivers.
I have downloaded the files from nvidia website:

81.85_forceware_winxp64_english_whql
nForce4_amd_6.69_winxp64_english_whql

I can down load the files fine but when executed I get the message:
"The contents of this file cannot be unpacked. The executable you are
attempting to run has been corrupted.
Please obtain another copy of the file, verify its integrity, try again."

I have no firewall running except for the standard windows firewall, and
have tried downloading
from the different mirror sites too.

Windows Xp Pro x64
Nvidia 6600 GT (GV-NX66T128D from Gigabtye)
Gigabyte GA-K8NXP-SLI motherboard

Thanks