Look for a check box setting on the microphone tab of your sound card's mixer that says something on the order of "+20db gain" or "Microphone boost". Many sound cards require this before they will amplify the microphone to useable levels.
You didn't say, but if it's XP, most of the time you can get to this setting if you go to control panel, sound and audio devices, click advanced, select advanced again on Microphone. I *believe* that this is the generic way to access it - every sound card I've ever used has a device specific mixer that will generally also allow you to access the setting, but it's done differently for each one.
As has been mentioned, if you'd rather not guess what you sound like, go into an online arena (training works well), tune your radio 5 to your own id, and you can hear exactly what others will hear as you are testing.
Just remember that some changes wont take effect until you exit and restart the game, so to ensure best results plan to exit and restart after each one.
Hope this helps....
<S>
