If a player (Media Player, iTunes, foobar, etc.) still doesn't work, have you verified that you are plugged into a USB 2.0 port? Certainly the 3-year old Dell should have USB 2.0 ports.
1. When you look in Control Panel > Device Manager > Universal serial bus controllers do you see the word "Enhanced" associated with any of the USB Host Controller entries?
2. Do your XP installs have at least Service Pack 1 installed (SP1)?
If so, you might try a different USB port. However, it's odd that it's not working on two computers (unless it's the "Pandora" thing). I know M2Tech says that "HIFACE Kernel Streaming" should be chosen for the playback device under Control Panel > Sound > Audio tab > Playback device. Is there another HIFACE entry that can be chosen?
Steve