Well, lots of stuff factors in here.
First off, the forums at 2-pop.com will be of much use to you. Lots of people over there using FCP4 with various 24p cameras.
I'm going to assume you've got a DVX-100 (panasonic) or the SDX-900, rather than something like a CineAlta hi-def setup.
Short story - don't do anything. If you're mixing it with other footage (assuming it's 60i footage), just pretend that the stuff off the camera is 60i as well. Both of the cameras I mentioned do a 3:2 pulldown to tape, so the 24p image is recorded at 30fps (interlaced, so 60i). Assume you're not planning to print this work to film, you're not losing anything by leaving the timeline at 29.97 (the default) and forgetting about it.
If you were going to film, or you wanted to be able to have better-optimized streaming video for the net, what you'd want to do is remove the 3:2 pulldown. The panasonic cameras have two 24p modes - 24p and 24pA (Advance). Advance does a 3:2:3:2 pulldown to tape, whereas 24p is going to do a 3:2:2:3 pulldown. Advance makes it easier to remove the extra pulldown frames, while sacrificing some smoothness of motion when watching the 60i image. In final cut, you can choose from your device presets an option to remove Panasonic DVX-100 Advance Pulldown during your log and capture. This means final cut will automatically toss all those extra frames and give you native 24p video that you can use in a 24 frame timeline. If you shoot in 24p instead of 24pA, you can use cinema tools (included with FCP4) to do the same thing.
The benefits? For going to film, obviously, you'll have a cleaner timeline for your telecine. Just make sure whoever is doing your telecine knows how to deal with this kind of stuff.
For going to the net, you've got 6 less frames per second, and instead of interlacing you've got solid, progressive frames. In theory you can compress to a lower bitrate or have a higher quality image, as compared to the 60i source footage.
The limit is that you can't throw it in a timeline with other framerate video.
Long story short: don't do anything and it'll just work. (like a mac!)