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See > http://support.apple.com/kb/HT1651?viewlocale=en_US&locale=en_US#link3 As you can see, the Early 2008 MacBook supports 4 GB of memory officially, but you can install 6 GB of memory if you want unofficially. You can buy the memory in OWC or Crucial > http://eshop.macsales.com/shop/memory/MacBook/DDR2/
Respecting to the hard drive, your Mac supports a 2'5" SATA hard drive, and if you want, you can install a 7200 rpm hard drive without any problem. You can find here a lot of hard drives that you can install on your MacBook. 7200 rpm hard drives are faster than 5400 rpm ones
Respecting to the memory, any memory from OWC or Crucial will work with the computer, so it doesn't mind if you buy the cheapest memory you find in those sites because it will work.
Respecting to the hard drive, HGST hard drives have a very good reputation. Just select one and look at the compatibility to see if your Mac supports the hard drive. As you are interested in a 7200 rpm hard drive, buy a 7200 rpm hard drive