I'm using a MacBook Pro 15" running 10.4.8 and have a problem when using my Apple USB Keyboard (the macbook pro's keyboard works fine).

My problem: certain keys are mapped to input themselves plus a function key. (eg: return key inputs return and esc instead of just return) and I can't figure out if there's a specific keyboard layout to download to make this work, as this keyboard was never a problem with my ibook or old g3. I prefer not to download some 3rd party keyboard mapper.

The keys that are bothering me the most:

The Return Key (according to keyboard viewer, it's mapped to hit 'return' and 'esc' at the same time)

The Delete Key (keyboard viewer says it's hitting 'delete' and f5 at once)

The 4/5/6 & "clear"/"="/"forwardslash" keys on the numberpad (each is mapped to be hit together with the corresponding key two above or below it, so 4 and "clear" are together, 5 and "=", etc).

Oddly enough, when using a simple text box such as the one in this forum, the delete and return key work correctly, though keyboard viewer still shows them as being mapped with esc and f4. the number pad keys do not work correctly, regardless of whether the num lock on the macbook pro keyboard is toggled or not.

In other programs/contexts, hitting return serves as a 'paste from clipboard' and hitting delete serves as a 'back button' (eg: if i hit return instead of enter when trying to login to a user account, it takes me back to the list of user accounts, instead of attempting to log me in).

Keyboard info: Apple Pro USB Keyboard. Probably 1.5 or 2 years old. Has a kensington usb/ps2 wheel mouse attached, but problem persists if mouse is unattached, or attached to a separate usb port).

Things I've tried:
US & US Extended keyboard layouts
Switching the f keys to toggle software and hardware functions in keyboard prefs
Logging into a different user account
Searching high and low for help
Banging head against desk

Any answers or suggestions would be very greatly appreciated, because it's really killing me.