Thank you, again, pluggy.
I think I've read in other threads here that the 8U2 firmware update is recommended for connecting with Linux/Unix platforms. I don't recall seeing it mentioned in association with XP.
But if that's the only viable solution, I'll give it a go.
My biggest concern with this solution is the thought of supporting a group of new Arduino users associated with an open source shield I've helped develop for instrumentation of coffee roasters. Uploading new firmware to their Uno would be more than most of them signed up for.
Jim