Well, it depends on what you want to start with. First you'll need a dedicated connection such as a T1 or T3 (or if you have the bucks, an OC fiber connection). You'll need an IP address, netmask, gateway, nameserver, etc. too.
You'll also need to decide on the server specs. Under 1Ghz pentiums or AMDs are fine, but I would stick with 800Mhz or higher (they're cheap, so why not

). RAM will be paramount, get as much as you can, shoot for 512MB minimum. The next critical component will be the hard drives. I would recommend SCSI, IDE won't cut it for a server environment.
Next you'll need to decide on an OS. Your two main choices are UNIX (and all its variants) or NT. Most people would recommend UNIX or some flavor of UNIX.
I would recommend reading the docs and info over at
http://www.apache.org for some great http server software.
Those are just some of the basics you'll need to think about.