Use driver wizard on this months dvd edition or download a trail from click here
Scan the old computer and save the drivers to a folder. Now either copy them to c\d or take out the hard drive and transfer the files to your p.c. or write them to a cdr on your p.c.
Now format and install windows on the old machine. Either transfer the file from your machine to the old one or use the cdr as the source for the drivers.
This has worked for me a few times on real old machines without any drivers.
The other option is to load aida 32, pin point the peripherals and search for drivers. yuk.