Got throw away Del Dimension 3100, how to make it work

I am not at all computer guy.. Today I got a throwaway del dimension 3100 that my friends office were disposing off. I got the cpu and the monitor. The machine doesn't have any hard disk and the RAM, also it doesn't have any cables. I want to know If I buy the hardisk, ram and the required cables, will I need anything else? Will it be ready to use? I am not sure about the operating system? I would appreciate if anyone can let me know what all should I get to make it work.