A500-switch ?
/me tries to imagine THAT ;-)
O.k. serious:
I assume you got an A600 with a ROM-switcher that let's you select either
2.0 or an 1.3-ROM.
The A600 can take 2.5" IDE-disks out of the box (you'll need a cable too), or
3.5" ones (thats the normal size) with a special adapter (available from
Vesalia)
You won't be able to use more than 4GB with the 2.0 ROM, and I'm afraid but there
is no inbuilt HD-support in the 1.3-ROM (and I doubt you will find anything on
Aminet either).