Yew has many qualities that make it a prized tree in certain areas across the globe. Pacific yew has been studied, specifically the bark (i.e., taxol ~ compound extracted from yew bark), as a medicinal to fight cancer.
Poisonous parts of the yew plant include the leaves, bark, and seed (not the fleshy part). However, I've come across some conflicting data regarding just how poisonous the Taxus genus is...some Taxus spp. are not as poisonous as others according to a quick literature search.
Many resources categorize Yew as a good-excellent wood for heating. I could not find any mention of Yew firewood toxicity or poisoning. I guess my suggestion is to burn the wood and not the leaves! If you're concerned, I guess you could also strip off the bark and make sure the yew wood is well-seasoned (not green).