Upgrade PHP version to 5.3 on Ubuntu
Solution 1:
I used this tutorial http://atik97.wordpress.com/2010/06/12/how-to-upgrade-to-php-5-3-in-ubuntu-9-10/
Solution 2:
This was Discussed in ServerFault
Solution 3:
you should upgrade your ubuntu version. you can get the .deb files for new versions if you want to use apt, and pin them but you are likely to enocuter dependency problems.
please do a dist upgrade. the utility that does all the work for you in ubuntu is called update-manager-core
read up here
http://www.ubuntu.com/desktop/get-ubuntu/upgrade
and here
https://help.ubuntu.com/community/LucidUpgrades