Other tips: when dl'ing drivers from the Dell web site, do not use your laptops Dell tag to search for drivers. Once you enter in your 1720's tag (if it came with Vista), the XP drivers will no longer be visible to you.
If you've already entered in your tag and can't get to the XP drivers, remove all your Dell web site cookies and start over.
Burn the TPB OS image to a DVD if you can't find any 800 MB CD's. I went to a few stores and no one carries them any longer.
If you don't have a DVD burner then you seriously need to get with the 21st century