I know that I can add the SourceSafeTypeLib to a project and can explore it in object browser and find obvious things (GetLatest, etc), but I am looking for some more thorough documentation or specific tutorials on things like "undo another user's checkout" or"determine who has a file checked out.
If anyone knows where to find this material, how to do advanced or non-obvious tasks with VSS, or knows how to disassemble a COM API (so I can engineer my own api) it would be much appreciated.
You might check out Microsoft's documentation on the Microsoft.VisualStudio.SourceSafe.Interop namespace (I assume that's what you've looked at). I used it to create a VB.NET utility that does get latest, check-outs, and check-ins against a VSS 2005 database.
A quick perusal revealed the IVSSItem.UndoCheckout method, and the IVSSCheckouts type, which is a collection of checkouts for a given file.