All you people fussing about not having a 7200RPM when you have a 5400RPM. I don't understand it. I have a 4200RPM, 40GB in my laptop (should be slow as poo right?), and it suits me just fine. WOW is ok with it, Windows boots up perfectly fast, etc, etc. It's really nowhere near as bad as you think. Just keep the installed programs that boot-up with Windows to a minimum, and keep it defragged, and its fine. (I use O&O Defrag, check it out, it has a "Defrag by Access" option that defrags based on when files were accessed. So all your bootup files are stuck right next to eachother, and all the firefox files are right next to eachother, etc.) Doesn't feel slow at all.
At any rate now is probably the absolute worst time to be spending lots of $$$ on a harddrive. I'd wait a few months till they start cranking up the perpendicular recording tech and then make your purchase. In the meantime stick with the basic HDD that is included, get O&O, and see if that's not enough for you. You may find performance is completely acceptable; much more than you were expecting. I did.