For some time I have plugged USB drives, MP3 players etc. into my work computer (and maybe other computers) and have the machine find them, but not assign a drive letter so I cannot get at them. Frustrating!
Work computer is running XP Pro with several networked drives attached.
I thought something had gone wrong with the el-cheapo USD drives/mp3 players. Time to fix this, I said.
A bit of googling later and I was running diskmgmt.msc. Woohoo! Solved. Damn XP is not clever enough to know that it has to locate a free drive letter for the new USB drive and just tries to plonk it on an existing network drive and on failing, seems to give up. So I locate the drive in the diskmgmt window, manually assign a free drive letter and I'm away!
Nice to solve a problem.

Annoying to have lived with it for so long!