A few things to consider:
1. Do you want/need a second hard drive? With Macs, you have to get a firewire or usb external drive. With PCs, you can get a laptop with two internal hard drives. I've had two hard drives in my laptop, and I've been able to do songs with 50+ tracks of 24-bit audio for two years.
2. Core Duo is nice, but Intel is about to release Core Duo 2.66 and 3ghz models, and they're the fastest things out there, smoking even Athlon FX2s (see
www.TomsHardware.com ) - Might be worth the wait - get Live 6 and a faster CoreDuo in a few months.
3. Current Mac CoreDuos have heat issues. If you live in Texas, like I do, you don't need no more heat.
4. The cheaper CoreDuo PC lappies are priced nicely, but that's because the screens suck. Get a larger screen, especially for Live performances. Nothing beats high rez. With respect to screens, macs are easily the ones to beat. But boy do you pay...
5. Dell is cool, but also check out
www.SagerNotebooks.com and Mtech notebooks - these are both made by Clevo, and I would swear by them.