Got the SGI-propriatary VW320-specific drivers? Been a while, but the last time I looked there were some VW320 downloads available on SGI's Supportfolio site.
If you haven't already been there, SGI also has some VW320 info archived on their ftp.ftp://ftp.sgi.com/sgi/320-540/ntvidindex.shtml
There still is some info out there regarding video capture:ftp://ftp.sgi.com/sgi/320-540/uncompressed.shtml
and a clue as to which SGI-specific digital media modules (sgidmedia.dll, sgidv.dll, sgijpeg.dll, sgilivfw.dll, sgiqt.qtr, sgiqt.qtx, sgival.dll, sgiyuv.dll) and drivers (sgijack.sys, sgilivid.sys) were used by the VW320:ftp://ftp.sgi.com/sgi/320-540/QTdates.htm
Some of the VW320 drivers look to still be available on what's left of reality.sgi:http://reality.sgiweb.org/grossen/vw320/
And there's also a few "win2k" ssk patches on SGI's public ftp: ftp://patches.sgi.com/pub/win2k/
Looks like a number of the links are MIA, but there is a quicktime capture utility over in the programming examples folder:ftp://ftp.sgi.com/sgi/320-540/examples/index.htm
There's also a few additional mentions of the VW here:http://www.frontlinemedia.de/sgi320/