I need to fresh install a CentOS Then install some packages with some configs Then save all into a installable ISO. Is it possible to build it?
Yes. What you want to do is known as remastering the distribution. It involves mounting the iso, installing/removing the packages and files and rebuilding the iso again. Here is a tutorial.
Fedora can be easily remastered using a tool Revisor. I am not sure if it'll work with Centos or not though.
Long ago, I was installing XP, doing some settings on it, installing some apps and was making a Norton Ghost image, burning it down to a CD/DVD, and then I was able to easily restore from Norton Ghost. This was a very fast way to have your OS pre-installed, also saves time for installing on multiple physical machines....
Now, it does not work the way you were imagining it.
Basicly what you need to do is start reading about "kickstart" files. You have to put all of your customisations in a kickstart.ks file and generate the ISO with livecd-creator.
At the time of writing there is some guide: http://everyday-tech.com/create-a-custom-centos-iso/
Please note that building installation images(.iso,.img,pxeboot) for different distributions requires different approach. Debian(also Ubuntu) has debian-cd, CentOS/RedHat/Fedora has kickstart files