All too often I'm hired by the IT Department. First thing I usually have to do then is argue my way into the 'business side' of the company that hired me. After all, Architecture should be a business issue, not to condone IT strategy. Usually IT management grudgingly agrees.
But, when architecture is initiated by IT management, your work is a lot harder. I find it is really one of the hardest part in doing architecture: business often doesn't really care, and IT cannot sell the idea of architecture. You will have to overcome the suspicion of the business. That will take some doing, as nobody is really waiting for you. Make sure you're not on a mission to sell the IT strategy to a business that is a) not interested and b) doing a whole lot of other - more interesting - stuff.
So you really need to make clear to the business that what you're trying to achieve is aimed at achieving (long term) business goals. At the same time you need to stay on good terms with IT management, as they're picking up the bill for your hours. Another kind of trade-off than we're usually used to. The hard - but fun - part lies then in finding the balance between business and IT goals.
Sometimes you're in luck. Business is so pressured into change that it will welcome anyone who can assist them in realizing that change. But don't get used to it....