Ok, I have it!

You can see it
here.
But it only looks good when you have a table (I have a welcomepanel) above your categories.
I have put the lower border-images-code above the code in the forumhome_forumbits_level1_nopost-Template. So the welcomepanel have the Images from my first category *g*
The last category now have no lower border-imgs at this time. But its very simple, just put the border-images-code below $forumbits in the forumhome-Template.

Perhaps no comfortable way, but it works!

Sorry for my english, schooltime is a long time ago