Who ever told you that Windows XP media edition was more powerful than Mac OS X was smoking crack!
Where did you copy and paste those reviews from, CNET?
The statement that an OS is more powerful than a machine, XP more powerful than a PMG5, is ridiculous. That compares software to hardware.

There is no comparison at all. One is a virus magnet, full of security holes and a pain in the backside while the other is a stable, virus FREE, UNIX based OS.
I note that you compare the XPS 600 entry level price with the top of the line PowerMac G5 price. Hardly a level playing field. One has a Single Duo Core processor and the other has TWO Duo Core Processors.

Of course, your daughter will no longer be able to use Final Cut Pro or any of the other neat Mac only stuff if you take the Windows option. However, she will be able to run every one of the 114,000 known viruses available for Windows XP.

The G5 Quad is likely to be replaced shortly, probably around September, with an Intel driven version. (all Mac's will be Intel driven shortly). The new PRO versions will undoubtedly have two Dual Core processors (4 processors) in them and be around the same price as the current machines.

P