[CentOS] question on "yum --enablerepo=centos "

I'm installing Fruity for Nagios using the 4.4 Single Server CD and want 
to force upgrade PHP 4 to PHP 5 without having to upgrade everything on 
CentOSplus.

In order to install Nagios, I have to first enable RPMforge.  However, 
to use Fruity, I have to use PHP 5, which isn't included in the RPMforge 
repository, unless I enable CentOSplus and yum update/upgrade everything 
(which I did eventually, just to get everything working).

While in 4.x, I tried to enable *just* PHP with a command (something 
like) the following:

	yum --enablerepo=centosplus upgrade php*

After doing so, however, I got all these errors saying that it couldn't 
update it b/c other things were needing updating (Pear, I think, was one 
of them). Perhaps this had to do with me installing RPMforge and using 
protect-plugins.

Is there a way to force an update of, say, PHP and have also force an 
update on everything directly needed to install PHP?  I don't mind 
everything directly associated to the one package I need being updated, 
but I'd prefer to peg the other programs and not let them update.