billotos, welcome to FlyerTalk!

You can credit miles from any Star Alliance carrier booked at a qualifying fare for that airline/route, such as Lufthansa as you suggested, by putting your CO OnePass number in the reservation. wcalvert has given you helpful info on this in his post above.

As far as your second question, when the airlines integrate their operations, likely about March 2012, there will be seamless access to all flights which used to be operated by United or Continental, as/if they're continued, and they'll be offered under the new United Airlines name. There'll also be a single frequent flyer program which will integrate OnePass and Mileage Plus.

Whether you should start earning airline miles outside of United/Continental flights will depend on whether your future travel itineraries will be well served or not by concentrating on one major carrier or by needing to fly other carriers for some flights. Most FlyerTalk members find that the more one can concentrate one's flights on one carrier/alliance, the better one's elite status benefits are and the better the flight experience is. If one travels enough to earn top status in more than one program, of course, they have even more options.

Should you have a future simple question about the merging United and Continental, you can also use this thread:
http://www.flyertalk.com/forum/unite...-ask-here.html