Apple is beginning to invest in outreach to small businesses, but for this initiative to enjoy maximum success they'll need to understand the constraints that keep businesses dependent on Microsoft's inferior Windows platform.
Mainly it's a matter of time, or the lack of it; Windows keeps IT personnel too busy to investigate alternatives. Ironically, some IT departments still have a Windows-only rule, to avoid having to spend the extra time to learn to support other platforms, even though doing so might pay off in the long run, through reduced need for support.
Of course, time is just another word for money, and money is perpetually oversubscribed in any small business, the upshot being that it takes an iron will to consider total cost of ownership above initial price. Support somehow becomes a separate issue, subsumed under the necessity of having an IT department at all, and is effectively rendered a non-issue by (mainly voiceless) repetition of "that's what we pay them for."
So how to break into this circle of nonoptionality?
The first step probably has to be taken by the company (or IT department) itself, rescinding their Windows-only policy in principle. Until that happens, the best arguments in the world fall on deaf ears.
Once they've taken that step, other platforms can compete for their business on the merits, and once that's true new opportunities appear, as if by magic. Many of those opportunities will take the form of workstations that can easily be replaced by something else (a Mac mini, for instance), either because their users have no need for specialized software or because what they do need happens to be written in Java or some scripting language that will run just as happily on other platforms, or it runs on a web server and they can access it through any modern browser.
Those are the easiest sales, but there's another category that doesn't involve substitution but rather the insertion of a new layer, workgroup servers, into the company's network. I can say this with confidence, because Windows Server is so expensive only the most successful small companies will have seriously considered providing a dedicated machine running Windows Server for each workgroup. Others might be aware of the potential benefits that groupware running on workgroup servers can bring, but for most the cost of Windows Server will have proven prohibitive. Not so with other platforms. Apple's Mac mini server, for example, costs $1000, no matter how many client machines you connect to it, and it comes with the basic categories of groupware already installed.
Another selling point (for Macs) that shouldn't be overlooked is the relative ease of development of custom applications, presenting the possibility of crafting what you really need, whatever it might be, in-house, rather than making do with what you can find elsewhere. Microsoft has made the creation of simple databases and automated spreadsheets fairly easy, but beyond that you're pretty much on your own. Anyone with the skill to create an automated spreadsheet of more than trivial complexity can learn to build practically anything on the Mac, and well written Objective-C is self-documenting, so if they leave someone else should be able to pick up where they left off.
Of course, for the really tough cases, Macs run Windows just fine.