What follows is a simple double clickable method to handle this.
There are a variety of ways you can approach this problem: for example, iChat and Sharing preferences both have screen sharing options. In the case of my relatives, however, they all live behind NAT firewalls and even run old pre-screen sharing OSX versions, so setting up the needed tunnels or trying to port forward the inbound VNC connection on port 5900 through their firewall is a nightmare to do over the phone.
Instead I use the 'reverse connection' feature found in some VNC servers. I use Vine Server.app (formerly OSXVNCserver.app). But even this is painful to talk through for a computer illiterate relative, so instead I created an AppleScript that activates it with just a double click.
- Open AppleScript Editor.
- Enter this command:
where foo.foo.com is either your dynamic DNS domain name if you have one, or your IP address of your computer (not your relative's).
do shell script "'/Applications/Vine Server.app/OSXvnc-server' -connectHost foo.foo.com"
- Save this as an application (not as a script).
On your computer start up a VNC client like Chicken of the VNC and then place it to listen mode. If you have a firewalling router on your network, make sure port 5500 is port fowarded to your machine.
When they double click the application you sent, their desktop will instantly appear on your computer. Nothing else for them to do.
Thus the only prior set up you have to do is a one-time install of Vine Server on their computer and also to leave your double clickable AppleScript on their desktop.
You can if you like add a slight amount of security by using the over oscvnc-sever command line options to add things like a password or to use a different port.
A nice feature of this too is it does not require them to run the VNC server all the time. They just need to click it when they need me, so those security measures are not really needed.
[crarko adds: I haven't tested this one.]

