Hi @yugnats
First off, the circuit! What you described sounds great except did you remember to tie the ground from the Spark core to the ground of the supply powering the servo? Without that, it won’t work.
When you flash the above code into your core, it replaces Tinker, so that is not the way to go. With the above code, your servo should be moving back and forth.
If you want to control a servo from a web page via Spark functions and variables, see this tutorial:
There are some pictures of how I hooked it up there too.