Chess computers in human tournaments Do computers play in ordinary human grandmaster chess tournaments with time limits at 40 moves in two hours etc? If so how do they fare?
No, they don't, because it wouldn't be fair. According to Wikipedia:


  A recent top chess engine, Rybka, has an estimated Elo rating of about 3200 (when running on an up-to-date PC, as computed by SSDF).


This is about 500-600 points higher than an average grandmaster (rating 2600-2700). This would be the same rating difference as between a grandmaster and a top club player (2000-2200) - it is a totally different playing category.

According to how the ELO rating is set up, the expected score of a 2600 grandmaster vs. a 3200 computer is 3% - i.e. when they play 100 games, the grandmaster is expected to draw only 6 games. This is way too low to be interesting.