How can I write my own program to display my computer's information?

I’d like to create a program, possibly as a local web page file, to display information from my computer, like how much disk space is free, how many folders and files exist, what processes are running high, etc… What programming language would be the best for this? What other computer information is good to monitor?

Or is there a good program out there that I can download that does all this for me?

I am running Windows XP