Windows users of InDesign CS5 need to install two items into their Plug-Ins folder: there is an APIDToolAssistantCS5.pln, as well as a folder named (APIDToolAssistantCS5 Resources).
Bad things happen if you start InDesign with only one of the two items installed.
If you installed the APIDToolAssistantCS5.pln correctly, and the API menu still does not show up when you relaunch InDesign, go through the following procedure, step by step:
1) Exit out of InDesign CS5 for Windows
2) Remove all traces of APID ToolAssistant from the Plug-Ins folder
3) Start InDesign CS5 for Windows
4) Exit out of InDesign CS5 for Windows
5) Copy APIDToolAssistantCS5.pln as well as the folder named (APIDToolAssistantCS5 Resources) into the Plug-Ins folder
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