PHP 4.3.9 MYSQL 4.1.20 UPGRADE On CENTOS 4 With Plesk 8

I am planning on upgrading to php 5. I really don't need to upgrade to mysql 5 but do you guys think I will face problems with PHP 5.2.9 and Mysql 4.1.20 working together...

I am planning on doing the upgrade like this (if I decide to upgrade PHP and MYSQL all together)

1. STEP
nano /etc/yum.repos.d/CentOS-Base.repo

2. STEP
change the enabled=0 to 1 as follows

[centosplus]
name=CentOS-$releasever - Plus
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus
#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
gpgcheck=1
enabled=1
gpgkey=http://mirror.centos.org/centos/RPM-GPG-KEY-centos4
priority=2
protect=1

4.STEP
yum install php-xml

5.STEP
yum update httpd* php* mysql*

and restart the server do you guys think I will face any problems.

If I am only upgrading the php to latest I am planning on doing

1.STEP
I will do the 2.STEP above

2.STEP
wget -q -O - http://www.atomicorp.com/installers/atomic.sh |sh
yum install php-xml php-pdo
yum install php-pear
mv /etc/php.ini.rpmnew /etc/php.ini

and reboot