Installing php 5.3 on Ubuntu can be a bit tricky. Luckily, some kind *nix wiz made the following bash script that will downgrade your existing php 5 installation to version 5.3.

• Simply place the code below in a file called downgrade.sh (Or download it here)

• Set the permissions with sudo chmod 755 ./downgrade.sh
• Then run it with sudo ./downgrade.sh

And voila! Your PHP version will be downgraded to 5.3.

Disclaimer: Test out this script on a staging server first - it could cause problems! If it makes your computer explode, shoots down passing aircraft or sends shockwaves through the earth triggering worldwide volcano eruptions (or any other catastrophes)... Me and my keyboard are not responsible.