Sorry I haven’t got back on this sooner, been a little busy.
Basically, what you do is open Flash, and go to View – Grid – Edit Grid.
For some reason the default size of the grid is 18 x 18 px, so I always reset it to 10 x 10. Makes measuring a little easier. Then select Snap To Grid. This makes your cursor snap to the nearest point on the grid, which is handy for creating exact straight lines.
Then just draw a 3D style isometric box, so 2 boxes on the grid by 2. You’ll need to stick to a set scale though, otherwise things will look all wonky. Once you’ve got your box, you can put them together, cut away and add details to build objects.
If you’ve ever seen The Sims by Maxis, you’ll see what I mean.