broadband noise treatment is both an art and a science. it's easy to get rid of the noise and completely ruin your audio while you're at it. doing it right takes some excellent (and expensive) plugins and a lot of practice, not to mention a very good control monitor.
that said, if it's really just hiss (as in copied from inferior tape recordings) and your desired audio does not contain a lot of critical high frequency content, you may get away with just a moderate lopass filter type EQ.
stefan
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macpro 2x3 ghz dual core intel, 10.6.8, FCS 2