@JJ
I think he meant physically.
But by holding the 2 mouse buttons as soon as you turn on the A600 a menu pops up. Just hit any key on the keyboard and it becomes PAL, hit any key again and it becomes back to NTSC (this is just so that you can view the menu if your tv doesnt support one)........but to actually boot in one of these modes you have to select it in the menu, then boot.
now as for physically, you really cannot convert it. its not like the A2000 or 3000 or 4000, which you could supposedly change them by selecting a jumper.
In your case I think you may have to unsolder and resolder some chips.