Remote Assistance from XP to Vista

What are the things that an expert running Vista needs to know to
successfully help a novice running XP via Remote Assistance?

I support friends and family via RA. In the XP to XP world I found that
using Live Messenger was generally reliable. I have now upgraded to Vista
Ultimate. I get a variety of failue scenarios trying to accept invitations
now. No successes.

Most commonly, I get one of the following:
1. I accept the invitation. The novice gets a notice in Messenger that I
have accepted, but nothing else happens on either computer.
2. I accept the invitation. The novice gets a notice and a dialog box to
grant sharing permission. I get an indication that I am viewing the novice
desktop, but my screen is black.
3. I accept, the novice gets a notice in Messenger and I get an indication
that an attempt is being made. Eventually times out saying novice must have
stepped away from computer.

I can deal with firewalls, registries, and more. I find lots of snippets
here and there that give me clues, but can't find my way to a definitive
approach.

Can someone point me to a KB article or something else that could answer
this simple question.... What are the things that an expert running Vista
needs to know to successfully help a novice running XP via Remote Assistance?


-=Rich=-