Simple answer is, you don't. The RIAA have started putting a lot of kazaa "users" online with files that start ok but deliberately messed up with white noise in the middle. They have also started getting ISP's to fess up with user's names and addresses from IP addresses obtained on kazaa
The only feasible solution that i have seen suggested to date is a petition to the RIAA to create some sort of standard license or such (same idea as with TV license), where you pay a set fee and d/l all you want for a set time.
Check the low-down here.
http://www.eff.org/share/
It's a good read and some good ideas. Better to petition for this now, rather than being fined $100,000's just for sharing music