leaky valve covers.. decent size leak(s)

i see that leaking valve covers are a common problem. how do i resolve this annoying and filthy problem? i want to clean up my engine, but i cant if it has a perpetual leak.. i have to put a quart of oil in it about once a week. how bad is that? im not sure how much oil the motor is burning, it has about 128,000 miles on it, but i know the valve covers were covered in dried oil when i first get the car, and it still leaks around the covers.