Well....
I've switched computers a number of times, as well as switching hard drives. You can go the Slave route, but then you won't have the same apps already installed that you did on your old system. If all you're looking to do is transfer files, then don't bother even installing your old HD... just hook it up as a slave for a few minutes and dump the files onto your new drive,.. but if you want to keep using your old drive, it is entirely possible to use the old HD as your new master drive. Simply uninstall most of your detected items (video, sound, blah blah blah)... shut the computer down, pull the drive, put it in the new computer and boot it up... it will then re-detect the new hardware on the new computer and you can start using it again as if nothing had ever happened. Now,... if you run into any problems with the O/S (I assume you're using Windows) then you can run the repair disk and clean up any loose ends, but otherwise, it should go fairly smoothly. I just did this about 5 days ago and I now have a brand new computer with all new components using my old 40GB drive that I've been using for a year now... I didn't have to loose a single app or file. It is definiately possible... but like I said... if all you're looking to do is save a couple of files, then using your old drive just isn't worth it. Just back em up to CD or connect the drive just long enough to dump the files off of it.
WATYF