[CentOS] 5.1.6 php to 5.3, a few questions

Alright, looks like I have to do this (centos 5.x install).

Some questions..

1) I imagine I have to uninstall my current version of php...will yum 
remove want to take a ton of programs with it? Would I have to 
individually uninstall each package instead?

2) yum down the new version from some repo and then install it. I 
imagine nothing from the previous setup will be there and I would have 
to start going through the program and config files to make it work with 
my system, yes?

3) for those that have done it, how many things broke when you took out 
the old and added the new?

honestly just thinking about getting a new comp, installing centos6, 
adding some virtuals, moving the sites over to the new one and being 
done with it.

Not comfortable with a version of php that will not be backported like 
5.1.6 is with centos team.

any problems you encountered, would love to hear about them.

thanks