PowerPCs are much slower than the new Intel chips, the exception is the PowerMac G5 (the G5 was never used in a laptop). Now, I do believe that PowerPC computers will be supported for quite some time, but if you're going to have this machine for the next 4 years or so, you're going to want the speed of an Intel chip. Not only that, but today, Apple announced that the new intel macs can dual-boot in XP, for more information check out
http://www.apple.com/macosx/bootcamp/.
Just let me say this, those who already have PowerPC chips will fine, but if you're planning on buying a new mac, choose an intel mac, the speed will be worth it in the long run.