Although it is possible to run the .NET Framework 1.1 on x64 editions of Windows, you may be surprised to find that your IIS6 applications start failing with the following errors if you also have Exchange 2007 installed:
Links:
[1] http://www.techniquemicro.com/content/exchange-2007-and-net-framework-11
[2] http://www.techniquemicro.com/tag/net-framework
[3] http://www.techniquemicro.com/tag/64-bit
[4] http://www.techniquemicro.com/tag/exchange-server
[5] http://www.techniquemicro.com/tag/iis6