That's really odd behavior. I haven't heard of this problem before.
However, there have been a number of issues for both NM and Messenger on NT operating systems, primarily due to user priviledges or fast-user-switching. You can even get NM into a situation where its security certificate isn't valid (dunno how it happens, but it does).
- First thing is to verify user priviledges on both machines (assuming your folks use NT too).
- Next thing to do is to try to call directly with NM. Just enter your folk's IP address. If they don't know their IP address, it can be found in the Help->About box for NM.
If you can establish a two-way A/V when dialing direct, then there's something weird going on with Messenger. Try doing the same type of calling with someone else, and have your folks do the same...see if either of you succeed. There is a known issue with Messenger builds 76 and later that you cannot call from NM's Directory (Messenger integration) due to the "Trustworthy Computing" initiative...and the guys in charge of the NM server hasn't fixed it on their side yet. But connecting NM via the Messenger UI is still supposed to work fine.
If you still can't establish a two-way A/V connection when dialing direct, you might try re-installing NM. There's a trick to it, tho': you have to have your W2K CD, go to your INF folder, right-click MSNETMTG.INF and choose "Install".