Working with rounded corner example

I have been working through the rounded corner layouts in css sculptor 2 and I can't seem to get the results I am expecting. My content and leftcolumn are very much left justified. I thought that this might have been related to item 8 in the example, as my intersection for the dotted lines which matches ok, does not lie in the (0,0) co-ordinates as in the example. I have now done this excersise twice and still no go. If anyone has some suggestions that would be good.

Also everytime we want to add a navigation to a preset do we need to go through fireworks to deal with the rounded corners? Also can we only set up a navigation for the top and not left side, or for the left side presumably we just use a left column.
Kind regards
Julie Thompson