Not sure what you're hosted on, but, I'd bet it is FreeBSD based on where you're hosted.
http://www.freebsd.org/
You mention an 'old' machine, so you'll probably want the i386 version, grab the disc-1 and disc-2 iso files, burn to CD, boot from disc 1 and it should run you through a pretty basic configuration and get you up and running. I've not used their installation procedure in a while, but, they use a system called ports so that you don't really have to do any compiling. That may be menu driven by now. You can then install apache, mysql, php, ssh and ftp and pretty much duplicate your server. Assign it a local IP address on your network (you could even install X windows and use it to surf the web, use firefox, etc).
Once you've done that, you should have a decent development environment at home that you can pound on and experiment with.
You could do the same with Fedora Core, Suse, Ubuntu, etc.