You are using the boxed version of iLife 11, right? How much free space do you have on your Macbook?
First I'd run Disk Utility and repair permissions on your Macbook. If that doesn't help boot into Safe Mode and try running the installer from there.
This is a few months late relative to your post, but I just dealt with this. The full discussion is here - https://discussions.apple.com/message/18030492#18030492
Here's the short version of the solution.
I just got off the phone with Julie with Apple Support in Oregon. Here's the deal - Apple knew about this issue with the iLife 2001 installer "expiring" after March 23, 2012, so they put the workaround to release the block to installation in a software update which they issued March 17 this year.
Julie said that the oldest OS for which this fix has been included is OS 10.6.8.
She also said there are two ways to get this software fix - one of course is to hit the Software Updater under the Apple menu and download it that way - and she stressed that if you install your OS off an older DVD (for example, the system disks that came with your machine), you will need to run through Software Update several times, until you get the word that your software is fully up to date.
The other way is to get on Apple's site and download DL1512 - which you can find here:
"Apple Software Installer Update 1.0
This update addresses an issue that may prevent certain Apple software from installing. This update is recommended for all users running Mac OS X 10.6.8."
Having updated my OS, I retried installing iLife 2011, and voila - it installed.
So thanks to Julie at Apple Support!
Final note - The reason I had to reformat and reinstall my son's Macbook Pro is because he had installed Google Chrome and it tanked absolutely everything. The machine wouldn't even start up properly. Julie the Apple support lady said she has heard anecdotal reports about this.
I hope this helps.