on windows you can only get a grave using ALT codes (or copy and paste from the character map)
Under Windows hold down ALT while typing the appropriate number code on your numeric keypad to create grave accent marks. (note, has to be the number pad, not the numbers across the top of the keyboard)
For Windows, the number codes for the upper case letters are:
À 0192
È 0200
Ì 0204
Ò 0210
Ù 0217
For Windows, the number codes for the lower case letters are:
à 0224
è 0232
ì 0236
ò 0242
ù 0249