How to implement revenue sharing with users

Hi,

I've been lurking this site for a while, and find the content great. I'm working on a startup idea of my own. I've previously worked at large companies developing their websites, so I've got a pretty good idea of how to build the technical parts of it, but my concept kinda requires that i pay the users money.

I've previously worked with billing systems, and to tell you the truth, I'm scared beyond belief from working with these systems.

What I'd like to have, is an account system, where the users earn up money, and then once in a while, can request to get the money out.

How would i go about implementing that?

I'm curious about the following aspects a) are there any technical solutions that i can take and use already (low end (perhaps paypal?) to high end) b) Legal implications (will i be considered a bank, for instance.. I have no knowledge of what i need to be aware of) c) Fraud etc; i guess it won't be that big an issue if the users can only get money they've already earned up, but still.. fraud always comes up when talking about money. d) Anybody has existing experiences with this area?

Most of all, i'd just like to get a good overview of how to go about it, and what to expect, for this part of the project.

Oh, and, i won't say what the project is, because -- as everybody elses -- it's brilliant and never seen before... Well, perhaps not, but the above question should be taken stand alone.

Crosses fingers for good replies. Thanks.