I’ve done this before – running windows XP in vmware fusion on a mac(book), using the an apple super thin usb keyboard, somehow accidentally get myself into insert mode. Following the keyboard mapping advice on the apple site got me nowhere, but eventually found the solution as a post in the vmware forum:-
“On my Apple USB keyboard, I found that the zero key on the keypad (that is, the wide 0 key to the left of the period key) toggles insert mode in Windows XP.
If pressing this key generates a zero instead, try toggling Num Lock. On my keyboard, the “clear” button (just above the 7 and just below the reduce-volume button) functions as Num Lock.”