because you'll go round in circles.
The Toshiba is an excellent machine,and If you buy it you'll probably love it - it's a Toshiba after all - but I would recommend that you factor in the cost of another 512Mb of RAM while you're about it; the standard 512Mb isn't enough for what you want to do.
I have only read one review of the HP machine, and that said it ran hot when using the DVD writer, but then so will lots of laptops. It's very well specified, and I'm sure it's an excellent machine.
Both computers will be pretty hefty, but that probably won't bother you if you're after a desktop replacement.
If I was making a snap choice I would go for the Toshiba, but that's partly because I have always liked Toshiba laptops. It's your call, they are both very nice machines.