I've never quote seen this problem, but I'm trying to burn the ISO for Windows 7 with the Microsoft download tool, and it can't find the dvd drive. Unfortunately the tool does not give you the option to search for it.
The only thing I can see that might be it is in Device Manager it shows up as a CD-ROM. Yet the drive functions and burns fine. I just upgraded to latest firmware. Drive is Asus DRW-1814BLT.