[Users] Please advise a software for multipoint audio-video conferences

[Dmitry Lyubimkov]

There is a task to make multipoint video (and audio as a special case)
conference in a SIP-network. 
The SIP-network (on basis of OpenSER) works. We need the software for
creation of videoconference server (MCU in terms of H.323). Hardware
solutions cost too expensively 
We need software for the PC with general purpose OS. The platform can be
anyone - Windows, Linux... 
We are ready to buy for reasonable money if it will work. 
If anybody used similar products or simply faced - advise what to look
and where it is possible to buy. 

Dmitry