RealVNC has been around for a long time, and it is a great tool for remote control of a computer. I remember using it on servers back in the WinNT days. It runs as a windows service, so using the small client, you can connect from anywhere over port 5900 (the default).
For pair programming, it's essential that both developers are comfortable in front of their own keyboard, mouse, and monitor. You CAN use a single computer, but the developer who is reviewing has a bad angle on the screen and just generally isn't comfortable. Another method is to attach two monitors, two keyboards and two mice to the same machine. That would work (I've never done it), but after using RealVNC for two full days, I'm sold. It doesn't require a special computer configuration, and it's super easy to get set up and working. Your partner can know your VNC password, or (as I prefer), the partner turns on the listening client, and then I run the "Add a client" command, put in his computer name, and bingo!, we're connected. We're running on my box, but do an F8 and Full Screen, and you can hardly tell the difference.
I just finished 3 straight days of pairing, and we used VNC on the last 2 days. It works really well.
VNC is also great for conference calls. I was on a short conference call yesterday, and the folks on the other end needed to show us something. I turned on my VNC listening client, they added me, and we had video! Great tool!
If you aren't already using it, download it now. VNC goes beyond remote control well into collaboration.