New problem:

After all the tests get run on the Team City server, IE, in the full situation rather than in my little bench tests, the TASKKILL /IM iisexpress.exe command is not working, it's responding saying that the task cannot be killed and that I have to force it with the /F parameter.

I think it's probably because there are still things holding the web sites' ports open, like, the sites are still somehow active even though all the test are complete. The sites talk to each other so it's possible that this is the normal state for the sites, but now I have to figure out how to make them disconnect all their connections before I try to shut them down.

Any ideas on how to do *that* to a set of IIS express sites?