On our third try with USB to Serial devices, we found one that works (in a useful amount of time)!
Device Specs:
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Brand: ATEN (IOGEAR)
Model: GUC232A
Store: Best Buy
Price: ~$30
Website:
http://www.iogear.com/
Computer Specs:
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Operating System: MicroSoft Windows XP Home
Computer Type: Laptop
USB Version: 1
Must have CD-ROM drive for driver installation.
We plugged the device in while the CD was in the drive, the drive spun up, and it installed. We restarted. Voila, it works.
Good luck!