After upgrading the motherboard in a Windows XP system, I noticed that several new "Floppy Disk" entries had appeared under My Computer (the system had only one legacy floppy drive). I had installed a media card reader, and those entries appeared normally (as "Removable Disk X" etc.), but they were shifted down by several drive letters, so that what should have been "Removable Disk F" was showing up as "Removable Disk H". It seemed clear that the card reader had something to do with it...
The motherboard (Biostar A880G+) had an AMI bios which was autodetecting the card reader drives on startup. I had to search a bit, but under Advanced > USB Configuration > USB Mass Storage Device Configuration, I found a means to control how the card reader was handled. I couldn't turn off the autodetection, but I changed them all from "Auto" mode (in which the drives might be labelled as floppy drives) to "Hard Disk" mode. Saved, rebooted, and all the spurious floppy entries were gone! I then just had to go into Disk Management (Right click on My Computer, select Manage, then open Storage > Disk Management) to reassign the drive letters. (In the lower half of the window, you right click on the name of the drive you want to change, select "Change Drive Letters and Paths", and the rest should be obvious.