If you want to mix spoken text over music, try installing the Audacity 1.3 Beta and give the Auto Duck effect a try:
Auto Duck reduces (ducks) the volume of one or more tracks whenever the volume of a specified „control track” reaches a particular threshold level. It can be used to create voice-overs for podcasts or DJ sets, for automatic „ramping” of the background music in radio productions, and translators can use it to turn down the original voice as soon as the translation kicks in.
For the last Radio Netwatcher edition, I tried Auto Duck for the greeting. I recorded the segments, spaced them aprox. 6 seconds apart and placed that wa file below the music track I used (Propellerheads - Spybreak!).
Just mark the music track, select the auto duck effect, wait and voila, a perfect voice over: