1) There's no built-in defrag utility. And there's not too much out there.
2) Avoid ALL Norton products on Mac OS X. They cause far more problems than they're worth.
If you're experiencing "slowness", it's 99% more likely something else is the cause, rather than disk framentation.
However, if you really feel the need to defrag yourself, there's "Tech Tool Pro", which has a defrag utility, and there's "iDefrag".