thats pretty weird isnt it. i got the same deal.
1st physical drive installed, C:, D:, E:,
2nd physical drive installed, F:, G:, H:,
3rd phsical drive installed, I:, J:, K:,
removables: N:, O:, P:, Q:, R:, S:
opticals T:, V:
Network drive X:
And i have mystery drives designated L:, and M: in MyComputer on an Athlon powered system. I never really cared, dont think its ever been a problem, and basically totally forgot about it until your post reminded me of it
Go figure