Multiple monitor support is a funny thing.
On XP video dreams are limited to the primary screen only. This is for technical reasons.
But dynamic dreams can support multiple screens if they have been updated to support it on XP. Any of the dreams that I have been involved with should be updated and live on the site before the OD 2009 launch. Some of the dreams have also had a number of tweaks and improvements based on user feedback.
I have been told the other dynamic dreams will be getting multiple monitor support on XP at some point after the OD 2009 launch.
So the ones which will support multiple monitors on launch day are Ovals, Expanding Shapes, Winter Snow and Photo dream.
Will we ever support different dreams per monitor? Perhaps in the future.