Some previous threads to check out:
http://www.twoplustwo.com/forums/showthreaded.php?Cat=&Board=genpok&Number= 186902
http://www.twoplustwo.com/forums/showflat.php?Cat=&Board=inet&Number=159004
http://www.twoplustwo.com/forums/showthreaded.php?Cat=&Board=books&Number=1 90061
http://www.twoplustwo.com/forums/showthreaded.php?Cat=&Board=genpok&Number= 197446
Through these links, check out some posts by "Botman" who claimed, plausibly, to have made a successful bot for lowlimit online play.
Also, there was a fascinating article produced by the University of Alberta people that won a prize at an AI conference. The paper was about software they wrote to play "pseudo-optimal" headsup limit holdem. Theoretically using game theory you could play "optimal" headsup holdem (i.e. a mixed strategy against which no other strategy would have positive EV). However, the computing power to obtain the optimal strategy is much too large, so the University of Alberta team reduced it by several orders of magnitude by making some simplifying assumptions. Most of the paper was about why they thought their assumptions would not cause very much deviation from the true optimal strategy.