I remember reading a couple of posts about this on the dsl forum.
It sounded like it might be a pita.
I choose to use feather linux.Worked great.
http://featherlinux.berlios.de/usb-instructions.htm
http://featherlinux.berlios.de/about.htm
DSL seems to have a whole board dedicated to usb booting.
http://damnsmalllinux.org/cgi-bin/fo...gi?act=SF;f=17