If Microsoft have had it for over 100 years, why can't I get the bloody thing to work.

If I try and help my mate, by going through Live Messenger, it never works, I've only managed to get it working on internal connections, within the LAN, never over the net.

I wonder if this is why I have not heard of it before?

I've never had a problem with it - though recently I've been using web based apps like GoToAssist just because they're easier to use.

I think certain router firewalls can cause problems with MS Remote Access - although you'd have exactly the same problems using iChat.

Absolutely right.

There are many things that can go wrong, but provided Upnp is working correctly it really should be as simple as a couple of clicks. However, many people either disable Upnp on their router, disable the discovery services on their PC, or use security software which blocks the ports. If features are disabled or unsupported, then things don't work.