Many thanks to Robert W. Anderson for this solution.

In his post VS2005 PowerShell Prompt, Robert details how to create your PowerShell profile script which will add the VS2005 environment variables to the PowerShell process. Quite nifty.

As a note, after setting this up, you may get a message about how your script isn’t signed so it won’t run. One solution is to run Set-ExecutionPolicy RemoteSigned. I wouldn’t recommend going farther than that, though. It will allow local scripts to run unsigned and will warn you if a script that was downloaded tries to run. There are still vulnerabilities, so be careful. The other alternative is to sign your script.