Oh, I did not check if the link was still good... Sorry.

For communicating between two MCUs with wires is not to difficult. This page has several examples, look at ser2mod.bas and usart.bas for the basics.
http://melabs.com/resources/samples.htm

I think for you project I would go with USART because you may want tohave it working with an interrupt.

To help with the USART calcs and other stuff this is a very handy tool and the link is good.
http://www.picbasic.co.uk/forum/showthread.php?t=4994

Now for a really slick way of interrupting.
http://www.picbasic.co.uk/forum/showthread.php?t=3251

Let us know if that is any help...