You need a laptop-sized hard drive to fit in the A600 case. The A600 comes with a 2.x ROM chip so you can install that to hard drive. If you want 3.x you will need a 3.x ROM chip. If you want to use VisualPrefs and WHDLoad you will need an accelerator with Fast RAM.
[EDIT]
OTOH, you might as well just buy an A1200...
[/EDIT]
--
moto