XP SP2 (Loopback Address issue)
Remember this article ?
Programs that connect to IP addresses that are in the loopback address range may not work as you expect in Windows XP Service Pack 2
http://support.microsoft.com/?id=884020
With SP2, it lock down all loopback address except 127.0.0.1. This might affect quite a number of program including IIS5.1 if you binding it to other loopback address and so on.
You need to get the hotfix by ringing Microsoft PSS. But just know I found this download @ MS download site:
http://www.microsoft.com/downloads/details.aspx?FamilyID=17d997d2-5034-4bbb-b74d-ad8430a1f7c8&displaylang=en
This is the hotfix for the above KB, so you can skip the PSS call.