Installing snow leopard with lion went wrong

Hey everyone, I have a big problem: i bought a macbook pro in december with lion. I read online that its possible to partition the hard drive and install snow leopard on that partition and still have lion on the main drive. I decided to do this because i have a few programs i cant run with lion, but it went completely wrong. When insterted the first disk, it said it wasnt possible to install the software with lion so inserted the second disk. Something popped up saying i had to restart my computer in order to begin the installation. When it restarted, i saw the apple and heard the startup sound and then my screen was grey with a few weird black numbers and letters and in the middle a window saying: "you need to restart your computer. Hold down the power button for several seconds or press the Restart button." in several languages. I did that like 5 times already and i keep getting the same screen! What should i do? And most important, did my computer crash and did i lose everything on my hard drive?

 

Thank you so much for your help! I was afraid i had lost everything
Im trying to start up now in safe mode using shift but that doesnt work either! It stays on the apple, the disk (thats still in the computer, cant get it out) starts to make weird noises and after a few minutes it goes back to the "you need to restart" screen

 

Ok problem solved! Thank you very much i had to hold the option key to switch to my lion partition indeed.