Just go here:
http://mirror.ati.com/support/driver.html
then pick your OS. Then continue making your choices, the website will guide you through the process. Make sure to download the correct driver for your Operating System. I think all the Radeon family uses the same driver set, so you don't have to worry about matching drivers with your particular model.
Incidentally, I read somewhere online that this problem is caused by the video card drivers not being 100 percent Open-GL compliant. Evidently, No Limits does not recognize some ATI drivers as being 100 percent Open-GL compliant, even though you might not have any problems with any other games. Weird.