50D plus which other (40d?)

Hi all, I am interested in doing some wedding photography. At the moment I am far from good enough but intend on helping as a second shooter for a while.When (and if) I feel I have improved enough to go it alone I will need a second camera, but I intend on purchasing this now, as I want to be very familiar with both cameras at this stage.

At the moment i have a 50D. A friend is considering selling his 40D, which being so similar to the 50D really interests me.

Do I need a full frame to do weddings, or would 2 crop cameras be sufficient?
Thanks for input.

If you don't need it now, don't buy it now, as things always get cheaper and better. The 40D's a nice camera, I used two for a couple of years, crop bodies are totally fine. Having said that I do like the improved detail and high iso of full frame, but it's totally not necessary.

Thanks Tim