I've had the same problem as well. With mine, both drives (asus CD-S480/AH ATA device, and LITE-ON DVDRW LH-20A1H ATA device) show up as stated in device manager. The issue here is that it says the driver is corrupt. Here's the problem, when I uninstall the driver, and scan for new devices, it installs with the same driver

I just did the registry edit and am going to restart the PC now to see what happens....
*EDIT*
NO they do not show up when I go to Computer
Did this occur immediately after installing: within 12 hours, but it was after I installed Adobe CS3 Master Collection, I was about to install Microsoft Office and then this happened....
Does the drive letter show up when you go to Control Panel > Administrative Tools > Computer Management > Disk Management? no
Problem solved with the registry edit! Thanks guys!