Also, any potential system incompatibilities in simply swapping out these drives (despite both having the latest version of Leopard)?
There have been numerous issues with HDs in the aluminum unibody machines, for starters, read this thread (it's really long).
https://forums.macrumors.com/threads/729883/
But to sum it all up, some people have good results with one drive and others bad, even with the same drive/MacBook Pro model. For instance, I had lots of trouble with a WD Scorpio Blue 500GB, constant stalls, but great results with a Seagate 500GB Momentus 7,200 rpm drive, despite many reports of just the opposite. It is basically a trial and error thing, you pay your money and you take your chances. If one brand doesn't work, try another and use the one (ones) that don't in a USB case for backup. FWITW, people have reported good luck with Hitachi and Seagate 7,200 rpm drives and others with the 5,400 rpm WD Scorpio Blue.
Note: You must have a No. 6 Torx screwdriver to swap the knobs on the side of drive used to hold it in place, and a small + screw driver for the screws on the outside and the two screws inside holding the bracket over the edge of the drive. There are 2 different lengths of screws used outside, keep them in order so you can replace them exactly as removed and you should be OK. The manual that comes with the MaBook Pro has a diagram showing how to swap the drive, the angles used (yes, they vary) and the screw placement. As said above, beware, those short ones are really short, and I swear they are really looking for the chance to jump off your desk!
