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A billion here, a billion there, and pretty soon you’re talking about real money, Sen. Everett Dirksen of Illinois was reported to have said. He wasn’t talking about Microsoft.

Private antitrust lawsuits are piling up against our favorite monopolist, with Sun Microsystems’ recent filing only the latest. The possibility seems to be growing that Microsoft will have to spend some of its nearly $40 billion in cash to make the cases go away.

But would even billions in settlements be enough to deter Microsoft from its core strategy, which boils down to preventing or eliminating competition in any market where it can extend or leverage its Windows dominance? Or is the monopoly too pervasive?

The private lawsuits may be the best weapons left, now that the U.S. Justice Department and half of the states that proved the monopolist’s lawbreaking are acting like Microsoft’s in-house legal team. The latest federal judge on the case is behaving as if she’s more interested in rubber-stamping the department’s craven sellout, and getting the complex case off her docket, than asking serious questions about whether it serves the public interest.

Sun, AOL Time Warner and other plaintiffs have ample grounds to sue, and they should offer major thanks to the Justice Department even though the current occupants are doing their best to torpedo the smashing legal victory their predecessors won in court. Remember, the trial judge and a unanimous appeals court agreed that Microsoft is a monopolist and repeatedly broke the law to protect and extend its control.

Those findings, which not even the sellout settlement can change, provide legal underpinnings for the private cases.

One of the more interesting of those has gotten only modest publicity. Be, a Silicon Valley company that created a solid and innovative operating system, made its share of mistakes–a common thread among Microsoft’s legal opponents–but saw itself victimized by the monopolist’s predations.

Here’s a prediction. Be, now a shell of a company that exists solely to pursue the lawsuit, will settle for $200 million or so. That’s serious money for the Be investors, but pocket change for Microsoft.

If that happens, it’ll mirror another case. Just over two years ago, Caldera, a Utah-based company, settled for a payment from Microsoft after seeming to be on the way to victory in another federal court over allegations that Microsoft had squashed a competing operating system a decade ago. The settlement was reportedly in the vicinity of $250 million, though the companies didn’t disclose the precise amount–serious money for Caldera, pocket change for Microsoft.

Meanwhile, class-action lawyers are trying to extract big bucks, allegedly on behalf of overcharged customers. Still another federal judge tossed out a proposed settlement some of the lawyers had concocted with Microsoft, a deal that would have let the company solidify its monopoly in schools, where modest competition still lives, by giving away a relatively small amount of money and huge amount of software.

Sun’s case is about as surprising as seeing the morning sun appear in the East. Microsoft’s efforts to kill Sun’s Java software drew special scorn from both the trial judge and the appeals court.

Among Sun’s aims is to force Microsoft to bundle the Java environment with Windows, something Microsoft has refused to do with its latest version of the desktop-computer operating system. This would help Sun in its effort to provide a competitive counterweight to Microsoft’s moves to replace desktop software with “Web services.”

Sun also wants Microsoft to disclose information about the inner workings of Windows and other key technologies. In theory, the Justice Department’s settlement would require this, but the document is more of a giant loophole than a serious attempt to force the monopolist to treat other companies fairly.

Microsoft, which likes to brag about the billions it spends on research and development, still manages to add about $1 billion a month to its cash stockpile. It can afford to pay billions, if it must, in antitrust settlements while continuing its predations. It’s almost impossible to imagine the private plaintiffs turning down big money to force Microsoft to change its fundamental behavior. Asking competitors to be law enforcers is almost certainly futile.