The best thing to do is to search on eBay for one of the last ATX motherboards with ISA slots for the Hovernet card needed to run the desk. This way you can power it with a nice quiet/efficient PSU and a fast hard drive. It's only going to run Windows 95/98 so you don't need to spend much but it will make for a much quieter server.
This is a shame really cause it's a really nice desk.