You could buy Virtual PC 6.0 which has far better performance than any other version in the past, but I doubt it would be playable on that. Counter-Strike needs really video accerleration, and if you don't have it, forget it. Not to mention VPC doesn't even support hardware acceleration to begin with.
Fact: Buy Unreal Tournament and then download and install the modification Tac-Ops. That's Counter-Strike all over - just better. You won't regret it.
Or, you could find a used Orange Micro PCI card which houses an entire PC on a board, including a Intel processor, RAM and VRAM. Chances of Counter-Strike playing good on that are the same as Counter-Strike playing good on VPC.
Fact 2: No, you can't play Counter-Strike reasonably on your Mac.
I should also note that if you're attempting to use the PC version of Counter Strike on your Mac, then it will never open, no matter how much you shout at it. And, as you most likely know, there is no Mac version of this game nor will there ever be.