Yup, Sort out the finances first, make sure you get as much as you can.

As chip says, get video evidence of her in the sack, if the other bloke does actually like her and is willing to take her on full time then send him a copy of the vid, he'll be mentally scarred and everytime he thinks about shagging her he'll picture you taking her up the arse

But before you do this play with them for a while, don't let on you know until the money etc is swapped over, then leave it a few weeks, get a few pals together, invest in some maggy thatcher masks and go get sum!

Then once your satisfied, visit them at work and cause a raging arguement about how much of a slag she is, she'll never live it down and may have to leave her job