If you download the one for your card, they should. They are just technical demos made for your card, to show what they are capable of, usually for polygon and pixel throwing capability, into 1 character for example.
The latest ones are mostly showing off the inbuillt physics engines
I know for sure, if you have an ATI card, the ones from Nvidia won't work. They are built to use the specific GPU, so the program will realise you don't have that card, and throw you out of the installation.