Kazaa is doing ok. If the server says only a few thousand users are on, try disconnecting and reconnecting.
There are alot of users out there sharing junk songs (scratch noise). A great majority of people are still sharing good versions, but since kazaa tries to speed up your download, it'll download different parts of the song from 6+ different people. And if any one of those people are sharing a bad version, you get a scratch in the song.
But, no worries. You can still get around it. Usually, the only scratched songs you'll find are more poplular songs (if it's been on mtv or billboard's top 10 at one time or another, it's probably scratched.)
You can still get popular songs though. Keep on searching more, and sooner or later you may get a clean version of the song.
And keep your eyes out for a user who has a good version of the song and a fast connection. If the song works fine, you should right click on his name and 'find more from same user' check to see what other songs he has. they are probably all clean.
Eat. Sleep. Breathe. Ski.