In football, when you want to take down a big, powerful runner -- especially when you're smaller than he is -- you hit them low. Ideally, you and another player hit him at the same time -- one high, the other low.

Microsoft (MSFT) is getting hit both high and low now. From where I sit, Apple (AAPL) has achieved a dominance in the high-end spectrum that will only continue to grow, and I'm more convinced than ever that we'll see it make a substantial move into enterprise in the coming years.

For some time now, specialists working with advanced graphics, video/media, publishing, and complex gaming or CAD applications have been using the Apple operating system (OS) and machines. This trend has strengthened in recent years. With the superior hardware performance provided by Intel (INTC), more reasonable pricing, and the most efficient and stable OS on the market, I think we'll see further Apple OS penetration in enterprise, principally among those who are less price-sensitive and more interested in maximizing productivity per machine.

Now, as I speculated when Chrome was first announced, we're going to see Google (GOOG) go after the low end of the price channel. Chrome is now obviously an OS, not a browser. Not only do I think Google will be successful in capturing this low end, it may end up dominating it.

There's also the potential for Android to do the same in the cellular market. The only foreseeable obstacle facing Google as it penetrates the realm of operating systems may be  challenges from the Department of Justice (DOJ).

However, I think the DOJ will have a hard time saying Google is monopolistic for making a grab at a leading market share. After all, this segment is loaded with competition -- with various Linux resellers, Microsoft, Chrome, and even various versions of Mac's OS. (Even if Google does attain a market-leader position, that position would still represent a minority share --say 20-30%).

Moreover, I don’t think you’ll see Google bow down to the DOJ, as Microsoft did years ago. I think Google will fight the good fight if needed, and defend itself against charges of monopoly.

Lastly, while I can’t prove this point, my view is that Google has built a friendly, if not a strong, relationship with the Obama administration. So the foreseeable DOJ challenges may prove merely token efforts.

Bottom line: Microsoft is facing the most serious challenge to its dominance in years, and the threat is very real. I think Rome will stand for a while longer, but the pace of its inevitable downfall may be accelerating.