When dealing with online poker sites, it is imparitive to get the table/tournament number and hand number. The hand number are normally displayed on the top right or top left of the screen. Also, if the site has history, try to get a screen shot. This will help with situations like reporting abuse, collusion, etc.
If it involved depositing or withdrawing then make sure you keep record of the transaction number or print out the receipt. When you make a withdrawl you should get a tracking number. This will benefit you later on if, for some reason, you don't receive your deposit.
Just a little added info and helpful suggestions.
