I would still reformat the drive. Fresh install of Windows and programs. This will get you the best performance with your existing hardware.
If you only buy a new hard drive, buy something your bios(eprom) can recognize, make it primary and slave your existing 13gb to it. Then you can move critical files as necessary to the new drive. Backing up stuff is very good on older hardware. Most time they don't die a slow death.. they just quit.
