Hi, im working on a similar project.
But instead of having LED's on/off, i display numbers on the screen.

If the LED's and keypad the only device you'll be using, then you don't need a latch like i did.

You'll need a decoder to decode from the keypad into the data bus. The decoder depends on the type of keypad you have (the properties (e.g. 3 state)). You will connect the output of the decoder into the bus. The code you will write will just detect the interrupt coming from the decoder, and you will encode the value you obtain from the bus.

You can have the LEDs connected to port 1 (or any 4 free pins). Depending on the encoded value, you will just set or reset those pins in your code.

That's very easy



PS if you insist in using port 0 for driving both, see my next reply