I would suggest either downloading Audacity (which is free).
http://audacity.sourceforge.net/

Or you might be interested in Diamond Cut Millennium ($59) or it's big brother DC6 ($159). They specialize in audio restoration.
http://www.tracertek.com/index.asp?PageAction=VIEWPROD&ProdID=4 http://www.tracertek.com/index.asp?PageAction=VIEWPROD&ProdID=2 http://www.diamondcut.com/

Hope this helps.