in seriousness, your hard drive's speed has little to do with how the software performs, so the difference between the 5400 and 7200 is not going to be noticeable. what'll affect it most is your RAM. chances are, unless you have the need and the creativity to be running 10s of plug-ins at once, which, you don't, otherwise you'd be wiser and not asking on here, then even 1 gig of ram is plenty.
for making mashups, or producing dub step, which you probably will be doing, my 2.16 core two duo with 2 gigs ram is more than capable, so your brand new computer will be just fine.
maybe you could have googled for a second or two and found this though,
http://www.ableton.com/pages/faq/general_questions#faq_2_link
