I got as far as installing Snow Leopard and running all the updates. But... to upgrade to Lion, I need a minimum of 2GB RAM. My mid 2007 Macbook came with only 1GB, divided over two slots, 512MB each.
I figured I could just buy new, but I ran into two problems:
1: I can't for the life of me figure out whether mine is a 2nd, 3rd or other 'generation', while in the apple store, when selecting the right macbook, they only tell the generations, and not the year or model identifier or boot ROM version. Googling didn't get me an answer either.
2: if I do gamble and choose any of the early generations, it comes up empty - seems no RAM is being sold anymore for this old macbook.
So.. I wonder: is upgrading to Lion essential for security? And also, which generation is my macbook (boot ROM version MB21.00A5.B07, from mid 2007 (bought in June) ? Are there any other official channels to buy RAM outside the apple store online?