OK, this is an interesting / helpful piece of info.
I know it works in WinXP, not sure about other versions.
Sometimes, if you remove USB devices incorrectly, or with certain USB devices (those that don't have a USB serial number), you'll be left with "ghost" devices in your device manager. Well, here's how to see them. (Even if you don't think you have any ghost devices, this is a neat trick to see what else shows up.)
1. Bring up System Properties. (Right-click on My Computer and click Properties.
2. Click Advanced, then Environment Variables.
3. Under System Variables, click New.
4. In name type: devmgr_show_nonpresent_devices
5. In value type: 1
Click OK 3 times to get back to your desktop.
Now, the thing is, it won't show the ghost devices if you go to the Device Manager the normal way.
You actually have to go to START -> RUN and type in: devmgmt.msc
That'll open the Device Manager, now, click VIEW and SHOW HIDDEN DEVICES
You may be suprised by what you see. (Stuff that wasn't safely removed, and alot of stuff that doesn't have a USB Serial Number, so everytime you plug it in, it shows another instance of it.)
Just some useless / neat stuff we learned at work because the USB -> Serial cables would change to another COM port everytime you plugged it in again.