The BU-303 uses a Prolific PL-2303 USB to serial interface chip, so I reckon the Prolific drivers is all you'll need.
After that the device is a NMEA compliant device so should be sending standard NMEA sentences out a virtual serial port. I would expect it to be 4800 baud, probably 8-bit, with no parity and 1 stop bit.
You could try the US Globalsat BU-353 drivers, they might be backwards compatible.