How can I troubleshoot someone else's computer from my computer?

My mom is in her late 60s and gets very frustrated with her computer. I try to help her via email or the phone if I can, but I am very visual and find it difficult to understand what she is trying to describe (especially since she isn't sure of the names to call various computer-related items). Is there a program I can purchase (or download for free) that would allow me to view her desktop from my computer? I have something like this on my MacBook at work via Bonjour which allows me to do exactly this, but my mom has a PC and since I wouldn't be able to load personal software onto my work computer, I will have to use my PC at home. Any ideas? Thanks in advance for your help! :)