I bought a used 2007 MacBook for $80. It only came with 1gb of RAM and I needed something that I could use for basic web coding and photoshop/illustrator design. I read that although officially this model only supports 3gb of RAM it will run more efficiently if you upgrade it to 4gb (two 2gb sticks of RAM). So I acquired the correct RAM from a friend and followed this guide. I didn't have access to any "proper" tools at the time, but I turned the battery lock with my thumbnail and used a small flathead screwdriver from an all-purpose tool to loosen and tighten the screws.
The repair went very smoothly. I read the guide entirely before starting, and even looked up a video on YouTube just so I could watch someone do it. No problems were encountered and the RAM upgrade was finished quickly and easily.
My two main points of advice both involve inserting the new RAM. First, watch a video to make sure you're putting them in correctly, the little slit that's off-center goes to the left. Second, it's difficult to push the RAM in all the way. Don't be afraid to use a little force, the RAM should be pressed in until you feel some friction and it slides firmly into place.