Not sure what a good starting point is but you might want to try talking to a tax consultant who deals primarily with gambling. A friend has used these guys and seems pretty satisfied so far:
http://www.rbstaxes.com/
As far as whether or not you can offset any gains from poker with losses from flipping coins with someone, the answer is yes, provided you can supply adequate documentation [img]/images/graemlins/wink.gif[/img]