MagicDragon: macs can be ok .. they were a lot more expensive than pcs .. but i think the prices are becoming more equal now ? .. i never had a mac .. i love the freeware and games that are there for a pc ... i know very little games for macs
on a pc you can also use any linux distribution if you are into some finetuning of the os and want to have a stable environment (i still have to go there myself :))
when you plan on playing some games also have a look at your graphics card ...
in the past i thought the processor was the most important .. some years later the memory was the bottle neck which decreased performance when it wasnt enough so it was the most important .. now i think (as long as you have a decent processor and at least 512mb) the grapghics card will become the weak part which slows things down .. and probably the harddisk as well