su (sudo) command not found Galaxy S Vibrant I was wondering if any of you has seen this behavior:

I have an unrooted Galaxy S Vibrant and I was trying to root it permanently with z4root, unsuccessfully. While I try to do it permantly it seems to do it, but when I try to run Titanium Backup or any app that requires root permissions, it won't gain privileges. So, I installed a terminal app, and when I tried to run the su command it displays a command not found error.

My question is, what is missing from the OS? Any Idea? I know that you must have to be root in order to run certains commands but in that case it should display another error message?
The SU binaries are not included with the original distribution of Android, because they are not used at all by any stock system functions. Obviously, there are those of us that like to be able to do those things ;) Most rooting processes take care of this, but some leave it out. Hence the file @Matthew Read linked to should take care of your problem, if you follow the process he outlined :) 

If you'd like to read more about it, you can visit the Superuser website and find more downloads there, although the link posted supports Eclair, Froyo, Gingerbread, Honeycomb and Ice Cream Sandwich. So it should cover you :)