Adobe Evangelists use PC's to show off Photoshop these days? In the past, on high level functions in Photoshop, the Mac would clean the clock of a PC. Apple use to demo it when ever they would roll out some new hardware, and the PC didn't even come close to keeping up.
The Powerbook is a lot more than just flash. It's a great laptop. They do tend to run more money than a PC, but when you consider all the software that comes installed (iMovie, Garage Band, iDVD, etc.), it evens up pretty quickly.
On the other hand, for the same money, you can get a larger screen, more ram, faster processor, etc. The other consideration is Windows vs. OS X. Both are good and have their pluses and minuses. If you don't play games though, OS X would be my choice. (I would note that I play a lot of games, so I do have a Windows machine myself)
Finally, as someone else has already noted, if Photoshop and music compostion are your thing, I'd go with the Mac.