I was reading on Gizmodo earlier about Windows Home Server. Apparently, this is a flavor of Windows Server that is being marketed toward average users, with a focus on families. The idea is to facilitate the process of creating a cohesive home network. It is meant to provide easy backups, act as a file server, and even act as a web server. The OS would come pre-installed on server-grade hardware - boxes containing expandable RAID arrays and the like. That is what is intended.
Here is what I think: there is a reason that people who know what they are doing are employed as server administrators. Every service offered creates a new potential attack vector for prospective hackers. I shudder at the thought of someone who knows little to nothing about how a web server functions running one out of their house.
Plus, here is one of the core differences between a Windows client OS (e.g. XP) and a server OS (e.g. Server 2003): the server OS supports more than 8 concurrent SMB connections. The other main difference is that clients can't be domain controllers. That said, if you know what you are doing (that annoying caveat for which MS is trying to obviate the need), you can build such a setup using an XP computer; you don't need a Server OS for this since you probably have less than 8 computers at your house.