I would agree with De vinci on the mac as I have used both systems as well, but I would add an exception to it. If you plan on using the computer for anything other than studio, get a PC, as it has many more options available . Linux is more stable than W/98 and there are some great programs out there for it( thats not to say win 98 OS is a problem.
In last months Electronic Musician magazine the editors opening notes reported some problems he was having with the OS in his Mac, but macs have a gtood reputation for the studio. Hope I didnt completely confuse you here, I like them both. I own PC now because of cost considerations and havent been sorry for it. If I were going esoteric high end and money was no object I would have a Mac in the studio and a PC for home use.