There were 3 decisive games today. Karjakin defeated Felgaer. Ponomariov defeated Volotikin and Leon Hoyos defeated Cheparinov. All three games were very exciting.
Here are the current standings after 4 rounds:
1. 3.0 GM Hikaru Nakamura (18, USA, 2644)
2-4. 2.5 GM Sergey Karjakin (16, Ukraine, 2660), 2.5 GM Ruslan Ponomariov (22, Ukraine, 2723), GM Francisco Vallejo Pons (23, Spain, 2650)
5-6. 2.0 GM Lazaro Bruzon (23, Cuba, 2650), GM Lenier Dominguez (22, Cuba, 2638)
7-9. 1.5 GM Ivan Cheparinov (19, Bulgaria, 2625), GM Ruben Felgaer (24, Argentina, 2607), IM Manuel Leon Hoyos (16, Mexico, 2428)
10. 1.0 GM Andrei Volokitin (19, Ukraine, 2665)
Below is the official website of the event http://www.uaem.mx/ajedrez2006/index.html 
Chess Daily News from Susan Polgar
Leon played a very nice game today. He should make Mexico proud!
Naka as white was doing well when he played g4 and lost the iniative and messed up the position. that allowed black to open up the king side and white could not get the initiative back.
I think this was now the 3rd game of the 4 games with Nakamura’s game not being transmitted properly. last night it went down on move 21 and the game went to move 50. Hope they get the game transmission problems worked out.
It was great to see Leon win a great game. When it comes to chess you have to earn your respect by winning. A fine game.
tuesday.
Nakamura lost and Ponomariov won. Pono moved into first place. some games still going on. Karjakin lost so he did not move up.