PHP5

[Aaron Spiegel]

It seems to me that RPM installs of both PHP4 and PHP5 should go
pretty cleanly.  My only real concern would be making sure to backup
the httpd.conf in case the RPM install trys to replace it.  If they'll
go into different directories (not sure if this is possible-- don't
use RPM), you can even have them both installed, and switch between
them within the httpd.conf.

There's also a howto on setting up PHP4 & 5 side by side in O'Reilly's
"Upgrading to PHP 5" book, or a short answer on google groups: 
http://tinyurl.com/ce8tp .  A lot of hosting companies are offering
both versions through something like this.

On a related note:  PHP5 is a *huge* improvement over PHP4. 
try/catch, simplexml, and generic getter/setters will make you want to
never look back at PHP4.  Critics say its becoming more like Java's
other little brother (with derisive sneers), but I know I'd never go
back.  Of course once I get better at Ruby, I may not be going back to
PHP at all... :)

HTH,
Aaron