Hoo boy, I could give you stories about card reader problems with Windows. I work at a camera store, and EVERY time we sell a card reader, whether it's a Unity Digital, Phoenix, Lexar, or whatever, the customer calls us with questions.
1) Some card readers won't install unless they are plugged in before the computer is started. Don't ask me why. Other card readers (and digital cameras), won't even be recognized by Windows until AFTER the driver is installed. Try both.
2) If a device has an exclamation point in the Device Manager, the computer won't tell you a new device has been found when you unplug it and plug it in again. Windows "remembers" that a device isn't working correctly and refuses to re-initialize it. Unplug it, go into the Device Manager, delete the offending device, restart the computer, and plug it in again.
3) If you have problems where the card reader shows up intermittently, do a search in the Windows folder for "Diskmgmt.msc". Use this tool to assign a new drive letter to the card reader (doing it in My Computer may cause problems after a restart).
4) Many card readers are manufactured by 3rd parties. If you can't get the company's driver to work with XP, ask them if they can give you a reference driver from the reader manufacturer. That's what I had to do to get Unity Digital card readers working in Win2K. Those card readers are made by some company, like, "MST" or something.
5) Windows has to re-initialize a device for EACH USB port. Try to use the same USB port for each device. Switching between different ports (especially different USB roots), can make Windows tempermental.
6) Brace yourself and behold the power of Windows! :-D
That's all I can remember for now. Oh, and if you're using a USB hub, try plugging the reader into the back of the computer. Digital cameras, printers, and some scanners are REALLY fussy when it comes to hubs. I don't know about card readers.
