I don't know how to install a hard drive but I believe it isn't that difficult, however, I understand the Tyros2 is restricted to housing an 80GB size hard drive, whereas, if you bought a PORTABLE HARD DRIVE, you would be able to save many more registrations, styles and any USB sticks you have.
I do small gigs on a regular basis which of course, entails a variety of sets for each venue and because of this, I quickly accumulated several USB sticks, so I bought a 320GB Iomega Portable Hard Drive for £39.00,(size approx.3" x 5") copied everything from the USB sticks to it and now I work with it permanently connected to my T4 saving all Medleys, Dances, Singalongs, Registrations, various Music Finders and any Styles I've tweaked direct to it and then just disconnect and take it with me when I'm entertaining. This means I can quickly access ALL previous sets and of course, it is also a backup when the on board hard drive doesn't load what I've asked for (which happens all too frequently I might add).
Hope this helps in some way.
Audrey