Enterprise software has a bad rap because it's such a jaded business; decisions almost never get made for the right reasons, and the level of politics and bs is absurd.

From my own experience: unless you're doing something really special (and even then it's not guaranteed), it's tough to convince a large firm to license your product if you're a startup or 2, 3 man firm.

The best way, actually, is through the proverbial "back door", i.e. make versions available on the web or downloadable, and get a critical mass of employees within the company to use it.