Try bleeding the brakes first. Might help a little.
Our OB pulls like a mofo to one side when braking hard on the freeway. The Toyota T100 has warped front rotors, and it does a neat little 'wanna be ABS' partial lockup in the front when braking hard.
My Legacy has bad brakes in general. Pulls really hard to one side during some braking, but not all the time. I use the engine more than the actual brakes though.