If you haven't got the "studio" add-on (ie no multitrack) I found this on the net (to save me typing out something similar....)
"4) When recording your voice, consider the four variables of voice technique: pitch, loudness, pace, and emphasis.
5) Make sure that you don’t produce popping consonants. To prevent this, don’t talk directly into the microphone, but hold it slightly to the side of your mouth.
6) One more thing to check before recording your final voice slate is your peak level.
7) You can view this by highlighting Windows Mixer under the Options menu.
8) The peaks should be between negative three and negative one for both your voice and your music.
9) Once you’ve recorded your voice satisfactorily, save it on the hard drive of the computer.
10) Pick a piece of music that correlates well with your specific subject matter.
11) You should then record your music and save it onto the hard drive as well.
12) The tricky part is combining the two at the right ratio of music to sound. The optimum ratio of sound to music would be from 80:20 to 70:30, respectively.
13) Experiment with your recordings until you get a balance that sounds right. The goal is to have enough music to create an effect, but not so much that it overpowers the sound of your voice.
14) To combine your voice and music selection, open your voice file.
15) Highlight the waveform and push Ctrl+C, which will copy your voice.
16) Now open your music file, place the cursor at the point in your music where you would like your voice to start, and go into the edit menu.
17) Under Edit, select Mix-Paste. This will combine the voice and music files.
18) If the mix isn’t how you’d like it, go into the Edit menu and select Undo.
19) Adjust the mix paste volume accordingly, and redo the mix paste in the same manner. "
That should point you in broadly the right direction.