I would try Nature's Miracle for cats,http://www.eightinonepet.com/product...play=52&main=3
It really works at getting out the stains and smells. It works well on old stains as well, it might take a few times, but it will come out of the carpet. I even tried it on soda I spilled on the carpet and got rid of that as well.
I found it at Petsmart, it comes in 3 sizes. 24 oz spray bottles, 1 quart, 1 gallon. Needless to say, I all three sizes on hand. http://www.petsmart.com/global/produ...N=2033673&Ne=2