Using arduino with a Raspberry pi

I have an old laptop that drowned the other day so I wanted to take the guts out of it and use a raspberry pi for the cpu and was thinking of using the arduino to plug the track pad and keyboard into. I'm sure this is more complex than I originally thought but if anyone could help that would be awesome!

I'm sure this is more complex than I originally thought

I'm sure that it is, too.

but if anyone could help that would be awesome!

Help with what?

I'm just thinking if anyone has done anything remotely similar I would like to have a little help knowing where to start.