Hard drives are really cheap. Get a new one, now, and use a program like Norton Ghost to clone your current drive to the new one. Then, just plug the new one in as your main drive.
If you live anywhere near a Fry's Electronics, right now, they have a Maxtor 200 GB ATA 133 drive for $60 with no rebate. You'll have to check your local area store to see if this is available in your area.
When you build your new system, you'll probably want SATA drives, but the one you buy, now, will always be good for backup and storing files you don't need on your main drive.