HP-Compaq Presario 4406RSH

I have an old HP-Compaq Presario 4406RSH (PC133) Desktop that I want to sell or donate if that is not possible. This computer contains Windows XP SP3 as an operating system, it has a monitor that may or may not work and 512 MB worth of memory. As I said earlier, I want to be able to sell or donate this machine but the problem is that I do not know how to do it. I had never sold a computer before and I want to know how to sell an old computer like this Compaq? What advice do you have for me? Also, during the time I use the computer I often play dinosaur game. What do you often play?