Thanks everyone. Yes, I looked at getting a 'corny' setup, but then I saw the price. As another friend of mine saws. "Free's a pretty good price. You can't beat free."
He's basically going to lend/give me eveything I need to keg and serve beer. An offer I would struggle to turn down. Even if I only use them until I can afford corny's (assuming I don't get on with the sanke's) I figure it'll be better than bottling.
If I do change I guess I could then use them as fermentors. Hmm, or I could just ferment in one and rack to the other, then i would be able to produce the full 7.75 gallons. Of course I'd have to concentrate the wort so I could add water, but at the moment I'm having to do that anyway.
I was planning on using natural carbonation, I guess I'll have to put in extra sugar to allow for all the extra space. That's something I'm going to have to experiment with I guess.
Special thanks to kornkob for that answer, it made me chuckle.
wyzazz, you may well be hearing from me some time in the future with a few questions.