Myself and others have had a short diologue with Plextor Dirk over at Divx.com regarding deinterlacing and the ConvertX. The Wis chip in the ConvertX supports progressive and interlaced capture according to specs. However, there is no way ,at present, to disable the default deinterlace capture modes. Dirk has sent a couple users a "work-around" to test. This work-around is from Plextor engineers and an implementation MAYBE incorporated in a new release of Plextor's GoCap utility!
I'm hoping to keep abreast of this issue and really curious to hear results. If it works we may end up with much better captures eventhough they aren't that bad now.

p.s.
Many thanks to the experts here for educating me into video/dvd stuff. (good stuff- Lord Smurf and Reboot!)