1) Upgrade. I know you may not have the money (or are not willing to spend it all on a computer, like I do), but this will solve the problem for you.

2) A warmup-time. The Quake3 mod Urban Terror (www.urbanterror.net) has the option to have the game start, then wait a preset time (the warmup) and restart the map (everyone respawns, all buildings are restored to original state).

#2 seems feasible to me.