Pull up a chair and watch the show. Carl Icahn is back for another round of boardroom brawling with Biogen Idec (NASDAQ:BIIB).

On the heels of an announcement that he'll try to get seats on Amylin Pharmaceuticals' board, Icahn is also angling for seats on Biogen's board, after failing at a similar attempt last year. He's also trying to expand the board by one seat, and to move the state of incorporation from Delaware to ... wait for it ... North Dakota. Hmm.

I'm not exactly sure what Icahn expects to gain with the board seats, beyond his stated goals. Biogen remains tied up with both Elan (NYSE:ELN), with multiple-sclerosis drug Tysabri, and Genentech (NYSE:DNA), with Rituxan, so selling the company wouldn't be as simple as putting a "For Sale" sign outside its Cambridge, Mass., headquarters. A bidding war, like the one Icahn spurred to get Eli Lilly (NYSE:LLY) to outbid Bristol-Myers Squibb (NYSE:BMY) for ImClone, doesn't seem likely, either.

A long time passed between Icahn's arrival on ImClone's board and the sale he orchestrated there, so maybe he doesn't want to sell Biogen at all. Maybe he just thinks he can improve the company. I'm just not sure where the improvements will come from right now. Revenue was up 29% last year, while EPS rose 33%.

Yes, Tysabri isn't growing as fast as it was -- though 156% for the year is nothing to sneeze at. In fact, on the conference call, President and CEO James Mullen said it would be difficult for the company to reach its goal of 100,000 Tysabri patients by 2010.

That's certainly not a shocker to Fool readers; we pointed that out even before cases of progressive multifocal leukoencephalopathy (PML) started showing up in patients prescribed Tysabri. Biogen and Elan will eventually reach their goal -- Tysabri is still the most effective drug to fight MS -- but only time will cure patients' and doctors' fears of PML. Unless Icahn has a time machine in his garage, I doubt he'll be able to help sales of Tysabri much.

In the meantime, while Biogen isn't picking up as many new patients for Tysabri, it also isn't completely losing ground to competing drugs like Teva Pharmaceuticals' (NASDAQ:TEVA) Copaxone or Pfizer's (NYSE:PFE) Rebif. Sales of Avonex, its other multiple-sclerosis drug, were up 13% in the quarter and 18% for the year.

The company expects adjusted earnings to come in at $4 per share this year, a healthy 9% increase over 2008. Tysabri, not Icahn, is the future of Biogen Idec. That's what investors should be paying attention to -- even if it isn't as exciting.

An Rx for further Foolishness:

Biogen is an active Stock Advisor pick. See all of the Gardner brothers' current recommendations with a free 30-day trial subscription.

Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. Elan is a Rule Breakers pick. The Fool owns shares of Pfizer, which is an Income Investor and Inside Value selection. The Fool has a disclosure policy.