I should have mentioned that I solved this problem. I installed VS.NET 2003, the problem being that I installed the 1.1 SDK before I installed IIS. So IIS wasn't configured to version 1.1. I didn't know this was a problem because I just followed the installation instructions in order, silly me.
This tool took care of it and everything works fine now.
ASP.NET IIS Registration Tool (Aspnet_regiis.exe)