Linux on a Speedstream IDSL router?

Hey all.

Can someone tell me if it's even feasible to hack a Speedstream IDSL
router to get Linux and a firewall on it?

I have this thing lying around ever since I got ADSL, and was just
thinking how cool that would be. And it'd free up a computer, and take
up a lot less space! The sucker has 5 ethnernet ports, so it seems
like it'd work in theory anyways.

But I don't even know where to start looking. Tried a google search,
but nothing came up that was relevant.

Thanks,
John