I don't believe that IDPA has an exact weight for trigger pull in the rule book. the best I can find is "Internal action work may be used to enhance trigger pull as long as safety is maintained" I think as long as the pistol can be safely fired it should be fine but if an accidental discharge happens due to too light of pull I get the feeling you won't be allowed to compete. ever!
IIRC in USPSA production class it is 4 lbs of pull required. Granted I have never had a trigger pull test done at any competition.
Here is the rule book. http://idpa.com/Documents/IDPARuleBook2005.pdf
"They say you can't use a rifle or shotgun indoors because a bad guy will grab the barrel. Yeah? Well, he better hang on, 'cause I'm gonna light him up and it will definitely be an "E" ticket ride."
"Make (your attacker) advance through a wall of bullets. I may get killed with my own gun, but hes gonna have to beat me to death with it, 'cause it's going to be empty."
Clint Smith, Thunder Ranch