Keyboard key assignment corruption in Windows XP

It sounds like your keyboard is switching between a UK/US setting and a French setting - known as AZERTY (as opposed to QWERTY) from the first 6 characters on the top line of letters.

The Wikipedia page on Keyboard layouts shows that the Q & A and W & Z keys are swapped in these two layouts (along with a few other keys):

QWERTY:

QWERTY layout

AZERTY:

AZERTY layout

With this information you might be able to track down the application running when the switch occurs.