If you want to install the GAX/GAT July 2007 CTP, you have to uninstall the February 2007 CTP first. If you have troubles like me, these are the steps :

1. Uninstall all Guidance Packages
2. Uninstall Guidance Automation Toolkit
3. Uninstall Guidance Automation eXtensions. 

Uninstalling GAX gives me the trouble.  At the end I got a blank/empty dialog box with only a "OK" button on it.

To solve this follow the next steps

1. Check if all Guidance Packages are uninstalled
2. Run the CMD prompt in the directory where you're msi is located
3. Run "msiexec /x GuidanceAutomationExtensions.msi"
4. If that isn't working reinstall the GAX using "msiexec /fa GuidanceAutomationExtensions.msi"
5. Run again "msiexec /x GuidanceAutomationExtensions.msi"

This works for me.  (Txs to Greg Cool for these tips).

In a previous post I wrote about how you could create a VS2005 template. I also told you that there was a problem when using multi-project templates. This can be solved by using the GAT tool to create your template. If you never heard about the Guidance Automation Toolkit (GAT) or the Guidance Automation Extensions, I would like to refer the Guidance Automation community site. You are probably wondering why I’m talking about two products. Let’s make it clear. First you have the Guidance Automation Extensions. This is the runtime and must be installed on every machine that will make use of Guidance Packages. The Guidance Automation Toolkit is only needed on the machines of the architects or lead-developers or the developers who will create the Guidance Packages. In this post I will provide you a solution for the problem with the multi-project templates