I'm having exactly the same problem using the same camera and also CS3.

The presets on my project are 720P 23.97FPS, but when the import is finished it changes the frame rate in the project to 29.97FPS.

I've tried amending the frame rate using the 'Interpret Footage' tab, but this makes the sound go into slo mo - The picture is fine however.

Any help would be greatly appreciated.

Thanks