Stick this in one of the personal files (hotkey.rc prob is most suitable):

jKeyLWinKey "!Popup"

You'll want to check out the modules directory. You'll find all sorts of docs archived there from loaded (and previously loaded) modules. Except for jkey... hrmm. You can get the zip with the docs for jkey here.

Also, if you're planning on making hotkeys, jKeyUseHotkeyDef is defined in the personal.rc, so use the prefix *Hotkey, not *jKey. (That'll make more sense when you read the docs.)