So if you keep trying to install .NET 3.0 and keep getting an error during install (and looking at the Error Log link in the failure message refers to the Windows Communication Framework being missing), go look for a file named something like “dd_dotnetfx3install.txt” in your %temp% directory (in my case, that was at C:\Documents and Settings\[username]\Local Settings\Temp, but just open a command shell and type “echo %temp%” to find out what it is for your system/login). If THAT log shows something like:

[02/02/07,12:55:41] WapUI: ***ERRORLOG EVENT*** : DepCheck indicates Windows Communication Foundation is not installed.
[02/02/07,12:55:41] WapUI: Return for Windows Presentation Foundation indicates a successful installation. DepCheck indicates the component is installed.
[02/02/07,12:55:41] WapUI: Return for Windows Workflow Foundation indicates a successful installation. DepCheck indicates the component is installed.

Then you need to restart your workstation in Diagnostic mode with minimal services and then try the install. It should work.

Details are here in an obscure Microsoft forums post. The method I used, transcribed for your pleasure is as follows:

1. Set your system to start in diagnostic mode with some additional services:
1. Click Start, then Run..., then type msconfig. Click OK.
2. Click the radio button to start your machine in Diagnostic Startup.
3. Click the Services tab and enable the checkbox to the left of “Windows Installer“, “Plug and Play” and “System Restore“.
4. Click OK. Authorize your system to restart.
2. In Diagnostic Mode, do the .NET Framework 3.0 install:
1. When your system restarts, click OK to acknowledge the msconfig popup warning and set the msconfig window aside (or close it and call it back later to set you system to boot normally).
2. Now install the .NET 3.0 Framework. Install should go off without a hitch.
3. Put your system back into Normal startup:
1. When the installation is complete, recall or get back the msconfig window and set your workstation to Normal startup. Click OK.
2. Authorize your system to restart.

You’re done!