There will always be people who'll say you shouldn't do this or that on this forum but I don't personally think that it's up to us to judge what you do with your pc. Don't forget a copy of Kazaa was included on the PC Advisor cover disk not so long a go.
Now what you might be better off doing is this:-
Download Lavasofts Adware remover from click here and spybot from click here and install these. Now un-install Kazaa and run the above two programs. Now do a Google search and look for Kazaa Lite (make sure that it is the Lite version). Install this and you won't get any pop-up ads etc on your PC. Kazaa Lite looks exactly the same as Kazaa but without the rubbish.
Now if you've downloaded copyrighted software and installed it on your pc then you will and should have to pay for it. However, if its Kazaa that's saying you should pay (for what I don't know) then the Lite version will stop this.
make sure you have a good Anti-virus checker. Kazaa has it's own viruses which infect files in the Kazaa download folder and as a result are passed on when other people download off of you.
Just recently I went to a relative to see to there PC as they were having problems. After I built the PC for them and set it up (leaving them to install their software), they had forgotten to install the Firewall and Anti-virus. As a result they had 162 files infected by a virus downloaded from Kazaa.