There's a key on the keyboard called 'insert'. Right above the 'delete' key. Not really difficult to find. Press that once to change the 'overwrite' mode Word is in into 'insert' mode, and once again to toggle overwrite mode again.
The status bar of Word (very bottom of the window, starting with the page number) has an indication OVR next to the language indication (English or so). If it's black, Word is in overwrite mode. If it's gray Word is in insert mode. So you can always see what should happen.
Kees
This is driving my kids nuts!! When they try to make changes in ms word, it starts deleting what they already have typed. Don't know what to do, any tips? Thanks so much, Gwen (Hope I'm in the right forum.)

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic