Pick up a copy of Norton Ghost 2003. It will support USB 2.0 in dos. Then make a backup image of your hard drive onto your USB 2.0 drive (not a hard drive clone but an image.) Then make the Norton 2003 boot disk, which the Norton Ghost 2003 software will do for you, its as easy as put in a floppy and click a button. Get your Serial ATA drive and hook it up and have your USB drive plugged in and boot from the Norton Ghost 2003 floppy. Have the software use the hard drive image on your USB drive to restore the Serial ATA drive. Then try booting up with the Serial ATA drive.
**Oh and you shouldn't need any special drivers if you use the Norton 2003 boot disk with your Serial ATA drive. This may not be the case however with other forms of DOS.
***And worse case scenario this doesn't work. But you will still have your original 40 gig drive fully in tact and bootable as before.