I rock. I could not be more pleased with myself if I tried.
Have a 2007 iMac, was getting a bit on the slow side. Someone somewhere recommended adding memory. I was a bit freaked up because it involved unscrewing the back and pulling things out.
But I finally plucked up the courage, bought some RAM and replaced it. Went from 1GB to 4GB (max my machine will take).
It's like having a new machine. Bye bye spinny beachball. Switching between iPhoto/Safari/iTunes etc all super fast. Everything is so much better. It's brill! I am now back in love with it for an investment of £50. I think it will give us another 2-3 years of solid performance. Although I might have to invest in another external hard drive or two.
Here's the instructions on how to do it and here is the company I used to buy the memory.
I am not an IT bod but this was really much easier than I imagined and took less than ten minutes from switching off to switching back on again.