Hold down the key as soon as possible after the chime but NOT before.
This for a little more information: http://support.apple.com/kb/HT1455?viewlocale=en_US&locale=en_US
Don't worry too much about your data from the project, you always have your backup which you can use with another machine if necessary.
something fell on my MBP and it shook the laptop kind of hard. it was still working after that incedent. then i decided to restart it just to make sure that everything works properly. i did the command/option P and R rebooting to make sure that it would run just fine. yes it did boot up with the chime and all. but what is happening is that as soon as the apple logo pops up, the rotating icon never stops and the my MBP doen't proceed to opening up the system. is there something like a 'safe mode' boot up that i could do? i really need to have my MBP running because i am in the middle of a huge project. i really do need help.