Canon's EOS Utility software, which includes the ability to edit picture styles on your HDSLR, has not worked on OSX Lion since Apple released the new OS in July. However, Canon has just released version 2.10.4 which remedies this problem. Here's the deal with this new version:
EOS Utility is an application that brings together all of the functions required to communicate with the camera. Functions for downloading and displaying images, remote shooting, and camera control of each setting when an EOS DIGITAL camera is connected to a computer have been integrated. EOS Utility 2.10.4 Updater for Mac OS X is software that will install EOS Utility 2.10.4 on your computer or update a previously installed version of EOS Utility to EOS Utility 2.10.4 It is necessary that the previous version of your software have been installed when you use this updater on your computer.
This update is only for Lion. Also note that this is an upgrade to the software that came with your camera -- if you can't find the original file, you can try these steps.