Setup .NET Framework 1.1 on IIS 6.0 Windows 2003 Server

Running 64-bit Windows does have an affect on your ability to run ASP.NET 1.1 in IIS 6.  ASP.NET 1.1 only supports running in 32-bit mode.  Fortunately, IIS 6 on 64-bit Windows can run in either 64-bit mode or 32-bit mode.

The following steps to run IIS 6 in 32-bit mode can be found in our MSDN documentation:

1. Click Start, click Run, type cmd, and then click OK.
2. Type the following command to enable the 32-bit mode:

   cscript %SYSTEMDRIVE%\inetpub\adminscripts\adsutil.vbs SET W3SVC/AppPools/Enable32bitAppOnWin64 1

3. Type the following command to install the version of ASP.NET 1.1 and to install the script maps at the IIS root and under:

   %SYSTEMROOT%\Microsoft.NET\Framework\v1.1.4322\aspnet_regiis.exe -i

4. When we setup a fresh Windows 2003 Server we will not find this installation ASP.NET 1.1 file, we should download it from here
5. Make sure that the status of ASP.NET version 1.1.4322 is set to Allowed in the Web service extension list in Internet Information Services Manage


Reference: 
http://blogs.iis.net/tobintitus/archive/2006/06/15/asp-net-1-1-iis-6-0-and-64-bit-windows.aspx