many new video cards running under vista dont support whatever it is that dominions uses for rendering graphics.
I had a frame rate of one until I found the proper driver.
Getting drivers for 64 bit OS is challenging. You can also try installing dominions on for example windows xp and just copying that folder - it should work [I have installed my dominions on 64 bit Vista without any problems, I have 8800GTS].
I'm impressed you even managed to install Vista 64bit. I tried and couldn't reboot my computer more than 5 times without Vista crashing fatally, had to wipe the HDD and reinstall each time it was that bad. My impression was to leave 64-bit well alone until it's got a lot more support. I'd recommend a dual boot with XP and Vista if you can.
i think the 64 bit usually works well w/ new hardware - seems they put more work into making it compatible than XP-64 was. but, yah, i'd try a dual boot... gonna do that w/ my gaming rig when i get back home - just to have one machine with which to adequately compare XP and Vista.