I am totally new to google checkout. Out of curiosity what would be some of the architectures for a poker site using google checkout? On each poker hand played would it be possible to directly move money from the loser's google checkout account to the winner's. Would this even be advisable from a security point of view. What would be the google transaction fee for doing this on every poker hand?
Gambling and betting sites are explicitly prohibited by the Google Checkout content policies. Your account will likely be suspended and you won't be able to pay any winnings:
https://checkout.google.com/support/sell/bin/answer.py?answer=75724
If your site is for entertainment purposes only, i.e. no winnings, you may be able to use Checkout. See for example the Zynga Poker game which uses virtual currency; players pay for the chips, but cannot collect any winnings: