There is an insanely useful guest post on the Jason Cohen’s blog: Bending over: How to sell to large companies. It’s not about the sales magic, i.e. not about how to get a large company like your software and decide to buy it. It is about different technical problems that can occur on the way, including weird contract clauses, the curse of the purchase orders, and so on.
I’ve encountered all of those problems firsthand and thus I highly recommend reading the post.