I need to connect to clients

How or what is the best method to connect to clients computers so i can repair them. I have server2k and a 2k workstation. Most of my clients are XP. If i setup VPN will i be able to connect to my clients or is that for them to connect to me to access my server?

What are the easiest solutions so that i can tell my users over the phone what they need to do to allow me to connect?

I tried downloading ultraVNC but i don’t think i want my clients to have to install the server and and run it as a service.