Jeff, I have that problem as well. No matter if you install the Power Panel Plus software first, or let Windows detect it, then install it, Device Mangler shows "?" next to "UPS."
Here's what I do. Install the software. Reboot. Connect serial cable. Windows detects the UPS, I cancel out of Windows Wizard.
Go into Device Mangler and reinstall the driver, pointing to the PPP folder on the System drive. All is well at that point. Should we not have to go thru this? Absolutely. Does it work perfectly after this harrangue? Absolutely.
Since updating to WinXP Pro, I've had no probs w/the OS detecting the UPS on bootup. No probs at all.
Rarely under W2K it wouldn't detect...rarely though.