Tax withholding on regulated US sites?

Hi,

I've been trying to figure out what the Tax situation is for non-US residents who play on regulated us sites. From what I understand anyone who's physically in the state can play on that states' regulated sites, but I can't quite find out how/if these sites withhold taxes. So a few questions:

- For cash games, from what I understand taxes are withheld per session. Does this mean everytime you leave a table 30% of your winnings are withheld by the sites?
- If not the above, does the site withhold these during cashouts?
- I've been told it's possible to file for it and get most of the withheld taxes back? Is this true for those who are tax-residents in non-treaty countries?
- I guess you'd need a lawyer/tax accountant to manage this for you, are there any companies that specialize in working with poker players? any recommendations?

Hope this is the right subforum for this question.

THanks!