Hey guys, same problem here. The device is a usb to serial cable. Mine came off ebay with an installation disc with HL USB Driver on the label. Folders on the disc are: HL0108 (with an exe named HugePine in it), PL2303 (with exes for xp & vista) [The license agreement indicates that the manufacturer is Prolific Technologies but there's no clear indication what the drivers are for] Installation of the Vista driver doesn't enable to device. The other folders are R340 which contains an exe for HL-340 and the last folder is USB-SIM9.0.
I've tried installing drivers from all three folders to no avail, I'm assuming that the drivers (or perhaps even the cable) does not support 64bit.