Slow motion and Speed changes

I've got loads of footage of a BMX competition shot 60 fps in a 720 24p format. I've dropped this footage into a 24 fps timeline, so it's all in 2.5 slow motion.

What I'm trying to do is affect all of the footage so that it plays at regular speed (2.5 X the original footage), but then at certain spots get it to slow down and speed up for speed ramps.

What's the fastest way to go about doing this?

Thanks for your help.

You need to post some more info:

What codec? (Sounds like maybe DVCProHD?)
What camera?
What timeline format?
What machine are you working on?

Thanks for the reply.

The codec is XDCAM EX 720p24, but I shot at 60 fps for true slow motion
SONY EX-3
The timeline is the same as well, XDCAM EX 720p24.
I'm working on a mac pro 2 x 2.66 dual core, 4 GB RAM, NVIDIA GeForce 7300 GT

Thanks.