I remember back when I was a kid, my Dad received for Christmas a real nice set of screwdrivers. I really liked them. I used them all the time for: poking holes in jar lids so my lightning bugs could breath, as a paint can opener, chisel, cleaning the mud out of my shoes, digging up ant hills. One of the worst beatings I ever got was when I nearly burned through one when I was using it as an electrical switch for a 4-H project.
Your work computer is a tool. Certainly more important than a set of screwdrivers. Yet I see people abusing them too. iTunes, flying toaster screen savers, SETI servers, browsing to questionable websites, generally installing software that has no business being on a work computer.
Keep your computer clean and run routine maintenance on it. If it isn’t making you/your company money it shouldn’t be on your computer.