If you believe these guys:

http://www.overboost.com/story.asp?id=426

The tool they used to separate the ball joint is sold at Autozone for $10

It is called "Tie Rod End & Pitman Arm puller for Compact Cars"

I just bought one today but haven't had to use it yet (I will in a few days). It does seem a lot sturdier than those pullers with the hinged arms (which I've tried before with no success). Good Luck!