There is a history of Gateway battling MS.
Some of the evidence at the DOJ antitrust site is internal Gateway memos talking about their battles with MS over licensing and IE.
Gateway also was recently a (part?) owner of what's left of Amiga. They've been trying to look at other options.
I think Gateway knows they're in danger of becoming another Northgate. A pioneer in the business, often with fast machines with good bang for the buck, but unable to compete with other vendors with cost advantages. They're being crushed by Dell in the PC market now. Dell is in MS's back pocket, they likely get better prices from Intel (being larger and Intel exclusive) and MS (larger, more cooperative) than Gateway, so Ted and Co have to do something.
So I'm not really surprised that Gateway is going to be on the witness list. If they were willing to (privately) battle Bill and Co years ago when they were stronger, they have little choice now, IMO.
Whether it helps them is another question - they'd have to be willing to be pioneers if they want to be a large PC vendor betting on Linux for the desktop (I don't think VAResearch/Linux counts). Ted has taken some risks, but going Linux in a big way would be a bet-the-company wager, IMO, and I'd be surprised if he went there willingly.
Cheers,
Scott.