Deleted usr/lib/libxml2.2.dylib -- computer won't start
If you still have the Snow Leopard Installation DVD you should be able to solve the issue by booting from DVD and then open Terminal to copy the missing file from your desktop (which will be in /Volumes/however-your-disk-is-called/Users/Dash/Desktop) back into the correct location (/Volumes/however-your-disk-is-called/usr/lib/).