If it's within the network, I usually just use Windows Remote Desktop to handle things quicker. If the user must see what I'm doing, then I use Symantec's PCAnywhere (not free), LogMeIn or VNC. For VNC, I actually do use another method that doesn't require the user to do much at all. They just need to open up the program and double click on a specified line to launch the listening mode that faulty.lee mentioned earlier. For those that don't know about it already, you might be interested in SingleClick VNC:

http://www.uvnc.com/addons/singleclick.html