Let me see,
There's a really good page at http://www.webconexion.net/speedtouc...ch_330_usb.php
Follow that to the letter, but make sure you copy
after you've unpacked and 'make'ed speedtouch-1.2-beta1.tar.gz and change its contents as per the webconexion page.
(/usr/local/share/doc/speedtouch/ is where speedtouch-1.2-beta1.tar.gz 'make's to)
Also, the mgmt.o file it talks about is quite hard to get hold of - use this instead: http://speedtouch.sourceforge.net/files/firmware.bin
(you don't need to get speedmgmt.tar.gz if you get this)
save that somewhere, and tell speedtouch.conf where it is in the MICROCODE="..." bit.
Apart from those two things, everything worked for me (apart from the slow upload speeds).
Good luck. Hit me back if it all goes tits up.