No one insists on using XP. In fact, XP has NetMeeting already installed, although there is no entry point...XP users need to click Start->Run and type CONF. You're thinking of Messenger.
People on a downlevel OS can invite XP users (or any other Windows 9x/NT user) to a NetMeeting conference via Messenger. When the other person user accepts the invite, NetMeeting automatically launches on on both machines. You can also invite other Hotmail/Messenger users to a NetMeeting conference via NetMeeting's Microsoft Internet Directory (MID), which is a fancy name for "messenger integration". However, build 76 of Messenger v4.6 has a security fix that breaks MID integration...the workaround is to deny Messenger upgrades (stick with build 73 or earlier), and you can still fix the security hole by downloading the latest security fix from IE (MS decided to kill two birds when only one bird needed to get the rock in the head). Regardless of the security fixes for either product, inviting via Messenger still works...only MID is currently broken with the latest build of Messenger.
Unlike other OS', XP cannot invite other people to start a NetMeeting conference via Messenger...no entry point. XP (Windows Messenger) instead just exposes A/V, app sharing, whiteboard, etc directly from the main UI, and yes, these features are only compatible with other XP users. This is why you erroneously were led to believe that you *need* XP for video conferencing, when all you really need is a webcam and a fast connection.
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