I have been asked to create a site on which users can invite each other to play a game on a specific gaming console (X-Box or PS3 for example). If the players do meet online and play, the site needs to monitor which of them won - then distribute prize money to the winner.
Can anyone point me toward a reference for monitoring the gaming results through some kind of API on these various platforms?
I can't speak for PSN or the PlayStation 3 (although I assume it works very similarly), but for the Xbox 360 and Xbox LIVE:
There is no single API that will enable you to access wins/losses for every multiplayer title - each title would need its own individual API.
Very few developers provide public APIs for their games with statistics for wins/losses.
Microsoft does provide registered developers (and some community members) with access to some Xbox LIVE APIs (which provide achievement, game, and profile related data).
So, what you want to build is not possible using APIs unless:
You are only tracking stats for one specfic game which does have a public (or otherwise accessible to you) API; OR
You are a registered developer and have access to some NDA APIs which provide the information you seek (for example, leaderboard information for XBLA titles, achievement/trophy data, etc.).
You may need to find some other method for verifying the winner.