I don't know how many ouf you guys are running IIS 5.1 on Windows XP to host sites but, I figured I'd run a couple things by you guys who are.
For starters, I'm running an Intranet website using IIS 5.1 on XP. We have (2) 2003 Server DC's but, it's not good practice to setup your IIS on your DC's.(simply because you don't want to chance exposing your DC's any more than you have to). So we took an old XP box and setup it up there.
It works fine but, I learned a few tricks along the way that I'm not sure you guys may know of. My guess is that you already know about the IIS Lockdown tool (if not, go here ). Also, by default, IIS 5.1 (which comes with XP) is defaulted to only allow 10 connections (other users will get an error if they attempt to connect past that limit). If you download MetaEdit 2.2, you can edit the metabase key MaxConnections for W3SVC and set it to anything less than 40.
As I keep learning more tip and/or tricks, I'll let you guys know.

I almost forgot to mention that snapfile has some IIS add-ons. One I was interetsed in was the IIS Password but after reading the EULA, it seemed that it came bundled with adware. Check it out and see what you think SnapFiles IIS Add-Ons