MAdCarters.com has made an excellent guide for how to setup Apache, MySql and PHP4 on your Debian box.
Read it yourself on their web site –
It's pretty easy to get a working local web server on your Debian box. You can use the command line (apt-get install) to get your packages or fire-up Synaptic to do it. When I set up LAMP I need my web server to work for various Content Management System (CMS) scripts. Some, like VTiger use gd for image manipulation, so I install that aspect when installing the web server. As well, I use Mambo for many sites, this one included, so I install php4-pear, curl, etc.