As you might have noticed from the install instructiosn, the install process of this pack is not similar to other CS5 products.
In case you are facing any problems while installing this pack:
1. Please make sure you follow the install instructions completely.
2. If you still run into any problems, please feel free to start a new thread in this forum, folks at Adobe would help you with the installation process.
Updated Install Instructions, check out the addition in step 3 that backup should not be placed within "Adobe Illustrator CS5" folder.