You don't need to override anything to populate an NSPopUpButtonCell in an NSTableView column. The thing to know is that you set the bindings on the NSTableColumn and not on the cell itself. Typically, you would have an NSArrayController in your xib that is bound to an NSArray containing all the options for the pop-up, and then you would select the column with the pop-up cell and go to it's bindings. Like in this screenshot (note the populated Content, Content Objects, and Selected Object bindings in the inspector on the right):
If you want a working example, you can check out this project I whipped up for another StackOverflow question. There's a bunch of unrelated stuff pertaining to making the NSPopUpButtonCell use NSAttributedStrings, but the bindings in the xib constitute a working example of how to bind an NSTableColumn with a pop-up whose options are populated by bindings.