Super simple problem you may run into when running Windows on an apple mac computer using the parallels application. You go to insert some text somewhere only to find it replacing the text instead.
Rebooting would probably work, or plugging in a keyboard with the INSERT button on it, heck, there may even be an equivalent keystroke on the small mac keyboard (I’m too lazy to google it right now), but if you want to solve it quickly, simply go into Windows via Parallels and click on START–Programs–Accessories–Accesibility and open up the On-Screen Keyboard. Click Insert from there, problem solved.