No, the model 4,1 Early 2008 MacBook will not be able to run Mountain Lion and Mavericks, but it can run 10.7 Lion. Lion is still available from Apple. You will have to call Apple Customer Care 1-800-692-7753 or 1-800-676-2775. to purchase it. Then within 3 days you will get an email with a code which you can use to download Lion from the App Store. The price is $19.99.
It's mainly the video card. The Models 2,1 through 4,1 have video cards with non-upgradeable 32bit drivers. The model 5,1 Late 2008 and newer have at least the NVIDIA GeForce 9400M with 64bit drivers. Mountain Lion and Mavericks require 64bit native drivers. Mountain Lion and Mavericks no longer support Intel's GMA 950 or GMA X3100 graphics processors.
While Lion used some 32 bit and a lot of 64 bit code, Mountain Lion and Mavericks are pure 64 bit, which excludes more systems than Lion did. It's not something you can add memory to, for example, as it involves the base architecture.
http://reviews.cnet.com/8301-13727_7-57470261-263/older-64-bit-macs-out-of-the-p icture-for-mountain-lion/?tag=mncol;txt
http://reviews.cnet.com/8301-13727_7-57387846-263/will-your-mac-run-mountain-lio n/