Yes, you need to do something. There are actually two things you can do - one is the "proper" way, but the other is much quicker. The proper way (assuming you recorded DVCPROHD and not AVCi) is to use the frame rate converter plugin on the footage to convert it to 23.98 (or 29.97).
The faster way (because it requires no render) - plus the only way that will work with AVCi footage - is to open the clip in Cinema Tools and conform it to the frame rate you want. (You'll have to reimport it into FCP afterwards).
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Jesse Rosen
Director of Technical Development
Abel Cine Tech, Inc.www.bustedskull.com