There is good DIY project for an USB interface/loader based on a simple but quite effective cirquit:

http://www.forumslader.de/12V-Versio...USB.209.0.html

It's in german, but at least the schematic is international:
http://www.forumslader.de/fileadmin/...an_Z-Diode.jpg

If you'll need a translation of a dedicated part, just send me a message...