ok this doesnt make sense to me. why would dooku say that the sith lord was in control of the senate? yoda and mace doubted that it was true so maybe it would be some kind of way to cover it up but that doesnt make sense, it just led them in the right direction. they even said they will start watching the senate closer. lets think, in control of the senate, hmmm maybe Palpatine! come on yoda. so the dark side clouds things but maybe dooku wants them to catch on for some reason. oh well they are all going to die in the next episode anyway.

I think it's highly likely that Dooku told them the basic truth about Sideous/Palpatine in order to create distrust between the Jedi council and the Senate. As for the suggestion that he wanted them to catch on to Sideous' plan, I think that may well be possible. As we know, the Sith can see the future, so perhaps Dooku had a vision of Palpatine casting him aside in the future in favour of Anakin.