Purchased this game several days ago and I tried to install in my Vista 64 bit. When I try to install it, it gives me an error message that says that the program is not compatible with my 32-bit or 64 bit version. I tried running this as an administrator and also with the UAC turned off...
No dice... any help would be appreciated... I got no response from GOG's custromer service...

Have you tried windows XP compatibility settings? You can set those by right clicking the shortcut and going to the compatibility tab. If that doesn't work could you please post the error message you are getting word for word? System specs and OS couldn't hurt either.
As for gog support did you contact them recently or has it been a few days? They are based in Poland so if you sent it off recently they probably won't be at work for at least another couple of hours.

The actual message is:
The version of this file is not compatible with the version of Windows you're running. Check your computer's sytem information to see whether you need an x86 (32-bit) or x64 (64-bit) version of the program, and then contact the software publisher.
I tried doing it under the xp compatibility setting and I get an error running the program message. Very frustrating... I thought that all of the programs are supposed to be 100% compatible to Vista 32-bit / 64 bit...,

yup, all three files are in the same folder

Bit of a longshot but have you ever had any of the spellforce games installed on that computer before? I'm thinking its possibly a registry problem with an older version of the game that doesn't actually work with vista 64.

Does the error come as soon as you try to run the installer or at some point durring install? It is possible that installer is so corrupted that Vista is not able to recognise it properly. You should try to redownload the installer (it's just ~2 megs) at least as on my XP the installer can be run alone but gives error as soon as it starts integrity check (about setup being corrupt, it does not seem to understand the bins are missing).
If all else fails I'd advice you to contact GOG tech support directly.

I downloaded the set up file and it finally worked. It appears that the setup file that I downloaded via the downloader was corrupt!
thanks for your help guys!!!