>I want to know for example on which of the two (for example) hard disks resides drive letter 'E:'. I wish to determine this programmatically, from my own program.

There is a correlation between the drive letter and device in the HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices registry key data. However, I haven't figured out what that correlation is, nor can I find an API call to get this information. Disk Manager seems to be able to figure this out, though, so there's got to be a way to do it.