Either one is fine, but I would chose Crucial over Kingston (just a preference). Make sure whatever ram you purchase comes with a lifetime warranty.
My warranty has finally run it's course and I feel it's time to take a chance & upgrade my Hardware in hopes of having a smoother running system (not that it's not running smooth now).
Installing ram does not void any warranty provided by Apple.
These are good online stores for Mac compatible RAM
OWC http://eshop.macsales.com/shop/memory/MacBook/DDR2/ - They offer Mac tested RAM at very good prices.
Crucial Memory http://www.crucial.com/ - good place to buy RAM from all over the world. They also have an excellent memory selector that allows you to choose memory based on your computer's model
Data Memory Systems http://www.datamemorysystems.com/apple-memory.asp - another good, cheap place to buying RAM if you live in the U.S.
Macdimms.com - Specializes in supplying Mac compatible RAM at extremely competitive prices. Brands featured include Crucial, Samsung, Hynix, and Micron. All brands carry a lifetime warranty. Discounts offered to educational institutions and students, active and retired military, resellers, and government agencies.
Here are instructions on replacing RAM in a MacBook with a removable battery. http://homeoffice.consumerelectronicsnet.com/articles/viewarticle.jsp?id=44404
If you don’t have the tools to open up the MacBook OWC has a set for $5