No stupid questions in video switching - it gets pretty complex.

The 990 will convert from s-video and composite to component, and while I haven't tried it I believe it will convert between s-video and composite video (so that a composite source like a VCR would be passed to the s-video monitor output).

It will not convert at all between analog video (composite, s-video, and component) and digital video (DVI) - the video processing involved would be expensive if you wanted to preserve the transparency of the DVI switching (and expensive even if you were for some reason willing to accept signal degradation across DVI). It will also not convert from component down to s-video or composite. Component is a much higher bandwidth video signal and converting down to composite or s-video would involve throwing away a lot of data to produce a signal that the lesser formats could use. Including this sort of conversion would add cost, and I don't believe that it would give any better video quality than simply using an s-video connection from the source - it might even look worse.