well.. i've used a pc, AND a mac for making sigs before.. the mac G5 HEAVILY outwieghed the specs of my other machine, and yet my 2 year old pc still ran better than the mac. the mac was running OSx, and had 2.8GHz(i believe, something VERY close to that), 1.5GB of ram.. while my pc has only 1.8GHz(overlcoked to 2.2GHz), 512MB ram, and a radeon9800 XT. i've used macs ALOT, and i still don't like them at all. sure they have a clean interface, but to ME i feel like i'm still missing something, that i'd get out of a pc. now, don't tell me i'm inexperienced with macs, becuase in no way am i. i actually know quite a decent amount about macs, since my elementary school only gave you macs to try and screw up. and oooooh boi, did i love turning security off on boot(hold space bar in boot, and disable the school's security software), then you can make the mac talk during class :-P haha those were the days, when you have a mac screaming "READY TO LOCK UP! macromedia dreamweaver WILL NOT OPEN!" haha... i got in trouble for that.. apparently, knowing more about the systems than the computer admin's at the school, is a BAD thing. meh... sorry for my rambling post..
to make a long story short.. find one of your old sigs that were made for you.