When going through a test installation of MOSS 2007 I ran into a little bit of confusion when it came to the .NET requirements.

1) Need .NET framework 3.0
2) Need ASP .NET 2.0 enabled in IIS > Web Service Extensions

So I downloaded .NET Framework 3.0 from Microsoft's website and installed it. I started digging around for the ASP .NET and found the below:

If you installed IIS before .NET 3.0 (or any other version for that matter), you will need to register ASP.NET with IIS using the following command

C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\aspnet_regiis.exe -i

At this point you can now go into IIS and enable ASP .NET web service extensions.