Hugh recommends ( hah hah ) the miranda desktop for remote monitoring of video output~:

http://www.miranda.com/?i=desktop_GC&l=1

one step down from this is the Kaleido

http://www.miranda.com/?i=multi-image&l=1

and some boxes from zandar also do multi-image composites:

http://www.zandar.com/products/index.html
http://www.zandar.com/products/dxcontents.html