I too have a samsung 612 dvd - originally b, upgraded to f using firmware.
It too ceased working under windows XP, but I have found the solution. I believe it will work for all drives:
Right click "My Computer"
Click "Properties"
Click "Hardware"
Click "Device Manager"
Click "IDE/ATA Atapi controllers"
Right click" Secondary IDE" (Or which ever IDE your DVD-Rom is on) and click "Properties"
Click "Advanced Settings"
In "Device 0" (Primary) or "device 1" (Secondary), depending on which your DVD-Rom is on, choose "PIO only" under "Transfer mode" (instead of "DMA if available").
That's it - should work now.
