Hard Drive assignment letters

My primary hard disc has 8 partitions (C-J). I have a cd/dvd unit (K).
I also have a removable hard disc with two partitions, which is attached
via a usb port.

When I attach the usb disc it becomes L and M, which is fine. However,
if it is attached when I start up, the first partition on the usb disc
becomes D, which screws up all the other disc references.

Is there any way around this, other than not having it attached when I
boot up?

Thanks.
--
Jerry Bank
Trenton, New Jersey
Music is the language of the gods.