The other suggestion are good, but
you are just putting a bandaid on it.
Unless the take was spectacular,
you should clean up the signal path
and re-record it.
You can't remove the hiss without
taking out some of the cool high frequencies
that you spend so much time and money
on mics, preamps, A/D convertors, etc.
I've used both the CoolEdit and Sonic Foundry
tools, and they work. I've also used the
tool that used to ship with EzCDcreator,
and it was no where near as useful.
transparent hiss removal is not
in the cards.