For best results with this tutorial, you hopefully have the following.

Basic knowledge of haskell and html.
A somewhat modern computer. I have a PIII laptop with 512M of ram.
A modern operating system. You should be able to develop HAppS applications using windows, mac, or linux.
- Linux Notes: I work with the latest ubuntu linux distribution, which is currently hardy heron. Works for HAppS pretty much out of the box
- Win32 Notes: You may have to darcs get HAppS-State head, and/or tweak the cabal file.
If you want to create a public web site based on the materials here, I recommend getting either a private server (more expensive) or a virtual private server (less expensive) which gives you admin privileges to install the packages and software you need. I use the cheapest virtual private server plan at linode to host this tutorial publicly. I wouldn't try hosting a HappS project publicly using a shared hoster like dreamhost that doesn't give you root powers to administer your server. (Dreamhost is great for other things, like cheap storage for online images.)
More requirements are described in the instructions for installing and running this tutorial locally. However, if you have the basics ingredients above you should be okay.
Please let me know -- or patch the tutorial -- if I forgot something. I hate getting stuck on some finicky aspect of installation when I am trying to learn something.