Credit card merchant website

This is my friend’s website related to online payment processing merchant account and he is using version 3.1 of wordpress because his server is running on php 4 and the latest version of WP requires php 5. So, he is stuck for now and has a simple wp theme. Can anyone please let us know how we can make the site looks better even though not updating to the latest version? And it there anything important that we are missing by not able to update WP to the latest version? Thanks for your help…