Turns out that Google Talk server fully supports MUC, but, being in beta stage the conferencing capabilities are not advertised so that xmpp-compatible clients will not detect their presence. But it does exist. Assuming that you have google account and google talk/gmail access, follow these steps to create new conference.
Update: For some reason you can now create chat rooms directly without messing up wit the web interface: Any room with id private-chat-%8x-%4x-%4x-%12x and server groupchat.google.com will do. You can use uuidgen to create GUID for such room. Credits go to Ulrikhe for finding this out, thanks!
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