You can forget about this. Interlaced output doesn't work correctly with any of the graphics cards. Even if they output interlaced, you're not getting the correct interlaced fields of the source video sent. The only way to get good image quality out of an HTPC is to use progressive output, unfortunately...
Actually Alan, I think the fact that time has past would work against you on this one rather than in your favor. The market is most definately moving away from anything like what you're trying to accomplish-
I know that everybody suggests "search" - but there have been a couple of threads on this type of thing in the past few months. IIRC, the consensus was that you'd have to jump through so many hoops to try and create a 480i signal on the pc that any possible gains by using your external scaler would be lost.
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