|High end music tends to be firewire but usb devices exist. |
The hard drive is important but very few laptops offer really fast drives. I wouldn't let it be my first consideration..
The problem with most laptops is they are not intended to be fast, they are intended to be portable. The second problem is most systems come with Vista which tends to bog down the system. Things like Line 6 ux2 won't be as real time as on XP.
Most systems can use more ram, I'd look at the build in sound cards unless you have a good usb device already.
Could consider linux such as Musix and things like hydrogen and audacity.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10