Mac OS is not starting up

[Tarek]

Hello there,

This is what I get when ever I try to get start Macintosh OS X.



That didn't happen before and I think I know why. There were two updates available last night, 10.6.2 and Safari, I updated and restarted. It was installing updates but in the end it said that an error occurred or something like that even though the installation seemed like it completed.

I don't know what to do now and I don't want to re-format because I have a lot of important data on there.

By the way, I have an external HDD that is 160GB, if I make a backup on it, how much space will it take? Like a time machine backup or system restore or what ever it is called?

Thanks a lot.