Apparently, Office 2007 no longer has character overwriting enabled by default. Pressing the Insert key on your keyboard does nothing at all. While most rarely use this function, a customer was blaming his keyboard from nothing working properly. A quick look around showed that, indeed, pressing Insert no longer enables the overwrite function in Office 2007 (Word in particular was tested).

Microsoft has decided some time ago to turn off this function by default, because it is indeed rarely used - it's the first time I noticed it was gone, and have never received a question up until now,   ...