Yeah, XP names all class-compliant MIDI devices as "USB Audio Device". It could be showing up as that.
Also, do you also have the editor open at the same time (or another audio application)? Windows only allows for one application to be connected to a class compliant MIDI device at a time.
Also, it could be that you have hit the Windows XP USB device limit issue. It seems that once Windows XP has installed over a certain number of MIDI devices it will refuse to show any new ones until you delete some of the existing ones. The problem is that Windows considers any device you've ever connected to be a valid installed device (controllers, USB hard drives, etc) and it won't show you these installed MIDI devices in the Device Manager even if you select the "Show hidden devices" option. Perhaps you could use USBDeview to remove some of the old devices you no longer use?
There are also other ways to fix/work around this problem. They involve editing a registry file, so you'll need to be careful if you attempt a fix. Messing up a registry file can cause some major problems. Make sure to back up anything you wouldn't want to lose before attempting any of this. Here are a few links to various solutions to this MIDI device limit problem: http://www.vyzor.com/support/viewtopic.php?f=45&t=186 http://www.rme-audio.de/en_support_tech ... q_10entryd http://www.cakewalk.com/Support/kb/reader.aspx/20090210
So I would try removing some of those devices from the device manager and see if that might solve the win xp issue.