IMOVIE 06 HELP - Converted clips play too fast/audio plays too slow

[StringThoery]

I am a guitarist and I would like to record myself playing along to music in iMovie.

I record myself with the isight camera and record my guitar with garageband.
At the same time i am listening to the song off itunes through headphones.

After everything is finished i open iMmovie (06, the 08 version was crap!)
and import the 3 things,

Here is the problem. The iSight video and garageband recording line up perfectly. Everything is tight, my fingers in the video match what i was playing.

However, when i add the Itunes song that i was playing along to, it sounds a little slow.
At first it seems like i am playing in time. but bit by bit it gets more and more off time until eventually its so off time that it ruins the video.

Is the itunes song playing too slow?

Or

Is the garageband + iSight recordings playing to fast?

And whichever on it is, how do i fix it? No one else seems to be having this problem (maybe because no one records music tracks)

any help would be great.
Im on an imac (the new black one) with 2GB of memory and an intel core.

any help would be great!