ProTools doesn't really like anything less than a high clock Pentium 4 on DOS based gear and some AMD's had compatibilty issues. Centrino's should be ok since they are mobile P4's. Check Digidesign's website for compatibility or email them before you buy. Fill it up with fastest RAM you can. The more the better.
Doc is right about Sonar. It's powerful and easy, but you still need a good USB mobile interface. There are tons out there but most max at 24bit/48kHz sample rates (like the Mbox). The included software is usually very weak however. After you buy the interface and decent software, you're back to the price of an Mbox factory bundle w/ProTools LE.
I once thought a "Sweeping Arpeggio" was an Italian janitor.
