Depends on what you intend to use it for. If you look at CPU strength in most modern PC games, the requirements are rarely over C2D 2.2 GHz (Crysis - recommended, not minimal), some with more complex AI or a bigger amount of NPCs being processed like ARMA2 recommend C2D 2.8 GHz.
Most of the times even 3.0 GHz P4 suffices so you shouldn't have problems with your 2.66 C2D unless they start making games that suck the power out of processors but I can't imagine how.
Perhaps you use a specific piece of software that relies more on the processing power of your PC but again, I can't think of one that would cause problems with what you have.


