Customize arrangement of virtuals desktops

[Krugg]

Hello,

I've been looking for some way to change the arangement of the desktops on expose mode. Actually, i would like to have five of them, arrangement like a "+" sign, as you can see it right below :

..... [ ]
[ ] [ ] [ ]
.....[ ]

(Don't pay attention to the extra dots, i did the best i could !)

Does anyone know how to do that, and if that is possible in the first place ?
i'm using ubuntu 10.04 if that's any condition.

Thank you