Setting Up A Microphone

Ok, I've got a USB mic and appear to have set it up OK, as I can see the levels meter going up and down. But I get no playback from my test call on Skype. It can't hear me.
I'm on a Mac Pro with OSX 10.4
Any way I can test it? Anybody out there understand Skype and mics?
Thanks

sit at my desk and find out you smug little ****