Assistance with downgrading to PHP4 (from PHP5) - CentOS

I need help with downgrading the PHP version on my VPS. At the moment it is running PHP version 5.2 (I think), but some old software that I am using will not run in PHP5. While I move the sites to new software and my new server, I'd like to downgrade this server so that they can still run in the meantime. I'd prefer to have someone talk me through this over MSN rather than to do the work for me - I like to learn! I have upgraded PHP, but not downgraded. I'm a quick learner and promise not to be a huge pain in your butt. This is fairly urgent and I'd like someone who can do this with me immediately. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows? (depending on the nature? of the deliverables): a)? For web sites or? other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software? installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform CentOS. PHP5 -> PHP4.