iMovie Qs for Audio features and Overlapping Videos

[MoyashiMist]

Hi, I am new to iMovie, and although i have already figured out a number of things, i want to know if a few things are possible and how they can be done.

1. How can I cut certain parts of audio out and adjust to only part of the audio file i want to be played?(instead of playing the entire song, i only want sections. is it possible to split this?)
2. Can I overlap a video over another? If i cannot do this in iMovie, is there a program in Apple that i can use to do this?
3. Can I overlap two audio files together in iMovie? if not, in GarageBand?

I use a Macbook Pro 10.5.6, and have the latest iLife software (i think)

please help me out, thanks.