First of all, some cards provide software controls to do this, either in a centralized fashion, or per game. In some cases this is the ONLY way to set it. (E.g., a Viper II cheerfully overrides any requests from a program to enable/disable v-sync. You can only set it from display properties. And I have a feeling it's not the only card that does that.)
Second, many games have their own settings for that. E.g., in Unreal Tournament open the console and type "preferences". Then open the "Rendering" branch and work your way from there.
Moraelin -- the proud member of the Idiots' Guild