if you are daisy-chaining the FW drive, it must be connected in-between the SC48 and the Pro Tools computer. Don't hang the drive off the 2nd SC48 FW port.
FWIW, I don't think we officially support the Turion chipset for Pro Tools. If you have further issues with the setup you may want to try posting in the Pro Tools LE for Windows forum.
http://duc.digidesign.com/forumdisplay.php?f=17
-Mike