Q: macbook WONT STARTUP systermversion.plist temporary change of os x version

I saw this hack on some blog. Justin's i was in a rush and needed to download a program that required an os version greater than mine so i followed the instructions and just changed it so that it owuld appear like a higher OS. I dunno if this was a wrong thing to do cause i just temporarily changed it for a sofware that it would bave worked fine on mine but wouldnt install because of this. Anyway, i changed it back straight after but instead of typing 10.8.5 i typed in 10.6.5 cause i was in a rush. And now my mac wont start up. I can't reinstall os x. NOTHING. i need help. HELP