"yum update" will ask me if it wants to proceed. I have not seen a way to not have the prompt for Y/N? Is there a way to not prompt and just go ahead and do the update.
The documentation for yum shows a couple options to do this. use -y on the commandline, for an individual run, or set assume-yes in the appropriate config file for always-on. man yum, and/or read http://www.centos.org/docs/4/html/yum/
-- "They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety'' Benjamin Franklin 1775