Win XP and Remote Assistance

I want to use Remote Assistance to help my clients remotely. I cannot get a connection to them using Remote Assistance. I have Win XP Pro, ZoneAlarm Pro 3.0.83, LinkSys BEFSR41 Cable/DSL Router (firmware 1.42.3) with UPnP enabled on the Router and in Win XP Pro. I am using Windows Messenger 4.6 on my machine and asking clients to request Remote Assistance from Windows Messenger 4.6 and/or MSN Messenger/NetMeeting (for Win 9x systems).

What if any, ports, settings, etc. do I need to change toget this to work? Are there any settings my clients need to set?