Well, the only thing i know if is called systeminfo from the command line.
go to run on the start menu, type in cmd. You will see a window with the system prompt, type in systeminfo
this will give you when your xp was installed. Also how long your computer has been running since last reboot.
As for the number of hours your computer has been running? or total time running windows, I have no idea.
I am sure a freeware program will tell you that though, go to www.download.com or somewhere similiar that offers shareware programs. You will find something.