Do you have a MPEG-2 video codec installed?
To display video dreams a MPEG-2 decoder is required. Certain versions of Vista do not come with this codec. Software like PowerDvD includes this in it's install. Certain versions of Vista do not come with this codec.
Here is the info page on Deskscapes where you will find a link to a third party codec. https://www.stardock.com/products/deskscapes/downloads.asp
Unless there is some sort of configuration issue with SLI set ups that could cause a conflict with running dreams I am unaware of this is my guess for what is stopping you from playing dreams.
Anyone else have an SLI set up that runs Deskscapes?