Problem
IIS manager crashes when modifying ASP.NET 1.1 sites on 64-bit Windows
Solution
Here is a long and good explanation how to solve the problem: http://blogs.iis.net/wonyoo/archive/2009/06/18/workaround-running-asp-net-1-1-on-vista-sp2-ws08-sp2.aspx
Short explanation:
1. Create the Framework64 directory for 1.1 \windows\microsoft.net\framework64\v1.1.4322\config\
2. Copy the 32bit config to 64bit config location created in step 1.
Copy file from \windows\microsoft.net\framework\v1.1.4322\config\machine.config to \windows\microsoft.net\framework64\v1.1.4322\config\