Well... if the project is showing the red line, meaning that the clips need to be rendered, then the Premiere doesn't think that your clips match your project settings. Right-click one of the mxf files and choose Properties. Compare the reported image size and frame rate in the Properties window to the project settings. Hopefully, a little compare and contrast will allow to locate the discrepency.
One other gotcha with 24p specifically: you need to know what kind of pulldown you're using. I can't say I recall whether the 1080 shooting modes on the P2 cameras support both types of pulldown, but I know that the 720 modes definitely do. You definitely want to read the manual for your camera to understand all the different modes, and whether you're shooting in a native framerate or with pulldown applied (my suggestion: stick to native framerates where possible).
To clarify, there are two types of pulldown cadences: regular 2:3 pulldown, and advanced pulldown (I believe that's 2:3:3:2 cadence, but I'm just going off the top of my head at the moment). Without going into all the gory details, when using regular pulldown, in order to restitch the fields together to assemble the right frame back for display, sometimes the fields will come from two separate frames, which means that it requires two decompressions & one recompression to reassemble the correct frame for display. With standard DV, this is fast enough that we don't bother displaying the red bar, but with HD footage, it's enough of a performance hit that we flag is as requiring rendering.
Short answer: 24p with regular pulldown requires rendering; 24p with advanced pulldown (ie 24pa) does not; and any native 24p (24pn) footage won't require rendering either.