Hmmm... if you have Windows XP on your system then you have "carte blanche" to any amount of accounts you like ....and if you have 2 computers then yes you can be logged on at same time.....
and i so hate the cheaters that do this ....but i've only seen this happen in play chip tables that 2 users in same household could sit at same table...I think they have better security on real money tables...
hope i cleared things up for you