Yeah, in a past life I was a senior graphic designer working on huge magazines, videos and websites.
Macs are for some, but since all the apps are on PC as well it doesn't really matter.
As far as the big list of software sbc posted, really very little of it is as mature as the closed source alternatives (or the Windows ones). Most of them are free, so the quality is fantastic for what you get, but things like the GIMP are more like Paint Shop
Pro alternatives than Photoshop. Ditto on Film-GIMP, Sodipodi, dia, Audacity and gCAD. The Mac / PC apps are much more polished and professional in that regard.
Linux is fine for people who need it, but when you are doing professional media stuff, by and large it isn't (yet, this is already changing at a dramatic pace, and I'm expecting Adobe to release a Linux version of Photoshop / Illustrator in the next release