This will be the hardest achievement for the game. At the end of the round, you will be shown how much XP you earned that round. You don't have to be #1 but you do have to be atleast within the top 15% to get the Gold Medal. However, this isn't just the room you are in, this is for everyone playing at the time. I got this achievement by repeatedly folding and getting smart fold bonuses (except for one time, I went all in with pocket jacks and won) and got 19,000 xp. The winner had about 29,000 xp so you don't earn a ton of xp to get it. I would say if you have 17 or 18 thousand xp you will get it. You will also earn some bonus xp at the end of the game so don't panic if you are short before the game is over. Also, make sure you do not leave the game before it shows the board. Doing so will cost you the achievement.
A good tip would be is to change your avatar to a female and play on the ladies nights. Since the majority of the players in Texas Heat have male avatars, a female avatar could give you an advantage with the extra XP.
**Note (22nd May, 2012): Despite the date, there are reports that the achievements are still popping.**