Actually, I've tried using old klunkers to do backups, and discovered that they can't take large hard disks. One of mine won't go beyond about 128 gig, tha other gets stuck somewhere between 2.5G and 80 G.
I have an old clunker that wouldn't take a big HDD so, being utterly penniless I with great trepitation flashed the bios. It's not all that hard and the box took an 80G hard drive no problem after that. Again, with apologies to this list, I loaded the box with win98 first so that I could use the bios diagnostic tool on the AwardBios (now Phoenix) website. I sent them 30 USD, they sent me instructions and some files to put on a floppy disk, I booted from the floppy and all was fine and straightforward. (Talk about a controlled environment-they knew my hardware and bios inside out and the OS was on the floppy- it jolly well ought to be straightforward.)
So if you're having HDD size problems, you know my advice! Regards, Max