How long should I leave it?

Ok a friend, not a particularly close friend but one of the people in my friendship group, recently split up with his gf. They were in an about 2 month relationship but werent as serious as people often seem to eb after that amount of time and as i am sure u have guessed by now i like the girl and actually think i have a fairly good shot with her.

I will definately talk to the guy before doing anyhting at all but how long would u think would be appropriate to leave it before i mention anyhting to him? and possibly how should i address it as i talk to him?

I don't think i've ever heard of someone good out with a good friends mate and getting away with it.

If you cant leave it, casually raise the topic in conversation, i.e. 'so how are you after that whole think with X?' and try and guage how he feels from there.