http://www.prolific.com.tw/eng/downloads.asp?ID=31

PL-2303 Software and Drivers Filename  Release Date  Version  File Size  

--------------------------------------------------------------------------------
  
wd_pl2303h-hx-x_v20019v2021.zip  2005/8/11    1471 KB  

--------------------------------------------------------------------------------
  
PL-2303 USB to Serial Bridge (H, HX, X) Installshield Driver Setup Program
v2.0.0.19 for Win98SE/ME
v2.0.2.1 for Win2K/XP/2003 (XP Logo Certified)
For Prolific USB VID_067B&PID_2303 Only
(for Mobile Phone, GPS, Modem, IrDA USB Serial Cable)