I run XP Professional and plan to buy a Harmony 880 remote control. Are there any usb based IR receivers that will work with XP Pro and the harmony 880? I've seen tons of threads regarding IR Recivers for Windows Media Center, but none for XP and the logitech harmony 880.

I want to be able to turn the computer on/off, and hopefully be able to play/pause/stop/etc DVDs.

I have a similar setup where I have the 880 and an HTPC running XPPro. The thing is you need more than just the USB IR receiver. You also need the software drivers for the IR device. I purchased the Streamzap ( http://www.streamzap.com/ ) remote control which cw/ IR receiver and drivers and the Logitech database includes the Streamzap. So it is fairly easy to setup the 880 to emulate the Streamzap to then control the PC albeit not perfectly. But it does work. Turning off the computer is no problem. The issue is turning it on. See this thread for more info [Link: remotecentral.com] The Logitech database also includes Msoft's MCE remote. You might be able to pick up the MCE IR receiver on eBay but you still need to get the drivers.

So... the answer is that the only way to do it is to have a MB that supports a Wake-on effect. Would that StreamZap one support a USB wake-on effect if the MB has it enabled?

Not 100% sure but in theory it should. I haven't actually tested that as I wanted complete power off. There are apparently some new MB or power supplies that support this type of power on that was mentioned in this thread [Link: remotecentral.com] see postings 11 and 12