I believe Inspiron is a Notebook, which would explain the standard notebook HDD speeds (5400 and 4200 - even my old toshiba 4.1GB notebook drive is 4200)
Check the Dell support page (should be a "Support" link on the Dell homepage) and it might tell you something about it.
If you want to test the drive on a desktop computer, you'll have to buy a 2.5->3.5 adapter (adapts Notebook drives to standard Desktop cable size and power connections) You can get one off of eBay for probably less than 10 bucks afters shipping, or sometimes your local computer surplus/misc store (not a chain-electronics store, as they dont carry jack-crap in small parts) and they might have it for sale, or let you borrow theirs. It's just a handy thing to have around when you own a notebook. I use mine fairly often, so i can re-format drives with a nice fast computer rather than my slow-a$$ notebook.
You're the guy from that hamburger train, right?