Why I can not install mac os x as usual?

i bought macbook it was loaded with 10.6.4...

and as usual i used my friend's original dvd 10.6.3 that came with another macbook 2009 to install a clean copy

i entered the dvd after bootting i get a massege says

.Mac os X can't be installed on this computer"

if you want to restore you system from a time machine backup click restore from back up"

i usually boot from cd by holding "C"

now when i hold "Alt" it gives me screen with "lock!" centered and password needed

i am so disappointed

any help will be very appreciated

best wishes.............

see you sooooooon