I still maintain that the best balanced team Aus have had for some time was in the last test vs Pakistan - 4 bowlers, an all-rounder, and 6 bats including Gilchrist.
At the moment, we have Warne and Lee bowling very well, half-fit McGrath, Dizzy, and no back-up. That meant 2.5 bowlers for all bar McGrath's opening spell.
McGrath (assuming fit), Lee, Warne, Tait/MacGill must be the attack for the next test and Watson should be drafted in immediately. He is almost a test class batsman and will improve as a bowler if he stays fit. For mine, he is the single most important cricketer for Aus' medium term future and my personal choice as future captain.
At least one of the batsmen must go to accommodate this. Rather than drop Katich as usual, Id open with him and punt Hayden, who seems to invent new ways of getting out every innings. Id like to see them play Hussey but drafting 2 from outside the squad is unlikely to happen.