XP and Vista drivers are already buildin for HP 720C. Refer to HP 720C Printer Driver for Windows XP / Vista for more information.
HP 720C Printer Driver for Windows XP / Vista
Download Epson DX4800 Driver
Epson DX4800 Driver
Download Lexmark Z615 Printer Driver for Windows Vista
20081105: Old link http://www.downloaddelivery.com/srfilecache/cjrZ500-Z600EN.exe not working, thanks Vedy for the info. New link updated.
Lexmark Z615 Printer Driver for Windows Vista
Download Lexmark Z615 Printer Driver
old link not working: http://www.downloaddelivery.com/srfilecache/CJXP600LE.exe 20080909: New link updated.