One way, is to get a laptop drive to desktop adapter (about $10-$15 at a local computer shop). Pop out the laptop\'s hard drive, connect it to the adapter, then put it in a regular PC. Format the hard drive as Fat32. You have some options now. Personally, I would put the system files on it (assuming the desktop is running Win9x, and the laptop drive is drive E:, you\'d type \"sys e:\"). Now, make a startup floppy from that OS, and copy all the files to the hard drive (as long as it\'s Win98, 98SE, or Me, you now have everything you need on the drive for it to boot, and recognize a cdrom drive). Put the drive back in the laptop. When you boot it up, select CD-ROM support. Put in your Windows install CD, and start setup from there.
If you have a Win9x CD, just run setup from the root of the drive. If you have a Win2k or WinXP CD, go to the i386 directory, and run \"winnt\". Also, it\'d be a good idea to load smartdrv first, so it won\'t take so long to copy files to the hard drive.