IIS7 and running .exe files

I'm using ASP.net 3.5 to run a .exe with Process.Start(). It works fine if I use the host that's built-in to VS2008, but if I use IIS7 it no longer runs. For testing purposes, I started just trying to launch Notepad.exe, so if I can get that to launch in IIS7, then I should be good.
I'm pretty sure it's new security that's preventing me from executing files, but I don't know exactly what.
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