I have 2011 13" Macbook Pro, i managed to make 2 partitions using a USB stick (which is partitioned and has Lion installer on one partition and Snow Leopard on the other partition, using it instead of DVD). Lion installed just fine, but when i try to install SL, pressing the SL installer gives me this error: You can't use this version of the application Install Mac OS X with this version of Mac*OS*X.You have Install Mac OS X 23.1. When i try to press alt when the Mac is starting up and choosing the SL partition of the USB stick, it gives me a kernel panic screen (press the button to shutdown and restart). Same with a boot DVD, pressing C when starting up. Any solution to install the SL on the partition?