No you can't. Some idiots don't realize, that the tag is not something you include in your name but it's something the server adds. It means also that you have to be registered to the server and the account is passworded. Different tags mean a different (registered) group, and different groups have different privaledges.
Well, first check youre mic is connected and that it works. You can do that by clicking the little speaker icon (=Play control) in the system tray. If you see a slider called microphine, you can increase volume of your microphone and be able to hear yourself speak (make sure the mute option isn't on). If the 'microphone' slider isn't in among the 'play control' sliders you need to go to settings -> advanced and you should be able to tic boxes. Make sure the 'playback' button is selected, and tic the microphone option. Click ok.
If you don't hear yourself your microphone isn't connected or it's broken.
Also, In ventrilo you need to check the setup window, and the first page there, voice. In the Input device dropdown menu you need to select your soundcard, don't leave it to default device. You may also need to select your soundcard from the mixer menu, select 'recording control' in the mux menu and 'microphone' in the 'line' menu. Then you can try and increase the line volume by using the slider below.
Then click the 'monitor' button and start making noise. The white box next to the monitor and test buttons indicate the volume level by a number, or, if you're microphone doesn't work / is wrongly configured it says 'Abs zero'
I've managed to sort out the problem, only trouble now is that I've pulled my back out and I don't think I'll be able to race tonight without being in absolute agony.