How to automate installer testing

I'm wondering if anyone has any best practices for automating the testing of installers on various machines with potentially different hardware / software profiles and by specifying various options to the installer. The idea would be that I could write "unit test like" code to set up a machine, run the installer, then test that certain things are true. Tests might look similar to:

Test:
    Boot Machine without IIS
    Run Installer
    Assert Installer Had Errors

Test:
    Boot Machine with IIS
    Run Installer
    Assert Installer Ran

Test_Fixture:
    SetUp:
        Boot Machine with IIS

    Test:
        Run Installer without IIS install
        Assert Website Not Installed

    Test:
        Run Installer with IIS install
        Assert Website Installed

I know I could create lots of VMs, but waiting for a VM to boot for each functional test sounds like way more work than I want. What I really want is a way to virtualize the installer environment. Any suggestions?