oracle server and client, How much memory?
You should be good to go with the memory that you have in your laptop. You will not require much memory, and assuming that your laptop is not ancient, you should not worry about memory problems.
512 mb is recommended by most for the server installation of oracle 9i i think.
Your best bet if you were worried about memory would be to make the swap drive of your linux larger. It is probably a gig or so, so you should be just fine.