Or get yourself a boot disk to use for the install. Most complete versions of operating systems these days have a bootable install disk containing all the drivers you need. Depending on how old is "old," Win98 is probably not a bad bet. Look on eBay maybe for a full version of Win98. You may need to format the drive before you re-install, as sometimes windows installations complain about installing over themselves, even though the existing install doesn't work.
Anyhow, you might need to format the drive before installing. Like Cliff said, find yourself a 10-year old to walk you through it. It's harder than say, adjusting valves, or swapping engines. 
Dan