Hi,
So many questions 
But I shall try to answer them for you!
What licences and software are needed?
OK there are quite a few answers to this depending on your status with Microsoft. So:
If you are an MVP, you can contact your Microsoft MVP contact and ask for a Live Meeting account.
If you are a recognised user group, then again contact your MS person in Germany, and ask about programs for getting LM.
If you are not either of the above, you can still get LM from one of Microsoft's partners, in Germany, that would be Intercall, BT, Meetyo, I think.
The way the LM 2007 licence works is that anyone within your company that uses or needs to attend meetings will need a licence. However, I'm guessing that the user group doesn't employee many people at all, and that you will be invite people outside of your own company. This means YOU need a licence, and not the attendees who do not work for your company. If your user group is more than 15 people in size, you may want to consider the LM Pro licence that has the event management, testing, survey tools, training tests, client/server side recording etc...
Does Microsoft support official User Groups if they want to broadcast their meetings?
See my comments above!
Hope this helps
Simon