The current version of Adobe Lightroom is 3.5, if you are on 3.3 I would first recommend updating to the 3.5 version.
The Macbook Pro mid-2009 13" model came with 2GB of ram standard, I would be worried that if you only have that installed, you are already at the minimum system requirements for Lightroom. To run Lightroom well I would personally recommend at least 4GB of ram, 8 if possible on a 64bit system. It is possible that your system may be trying to swap out physical memory with the swap file and that would increase your processor usage I believe.
Another question I have, is that you stated that your CPU usage is over 100%. What exactly is happening on your PC that has you concerned? Is the actual performance of Lightroom poor?
To help diagnose I would turn off all other applications after restarting the machine, and make sure it isn't an issue after a restart. This may help to find a memory leak within the application. If you are still having issues with Lightroom, I think your best bet is the Adobe Forums.