If LSU losses to Arkansas, they'd drop below bama and Arkansas in the BCS Polls. If it's a 3-way tie, the lowest team gets dropped. That would put bama in the SEC Championship against UGA (which judging by what my bammer coworkers tell me, they don't want to go).
If LSU & bama lose, bama would drop further than LSU (since it would be the #3 ranked team beating them, instead of a 4 loss Auburn team). In that senario, Arkansas wins the tie breaker over LSU, they'd play UGA in the SEC Championship game.
As for the BCS Championship game? Who the fuck knows, it'll come down to who drops the least (OU will beat OSU, VT could lose in the ACC Championship, etc., etc)