See, the Apple adapters work with the video card. You can't just do a split and have both a DVI monitor and an Svideo monitor from one DVI output because they are completely different signals. You can have one or the other. Maybe a splitter would still work to simplify the connections if you switched back and forth between the monitors.
You really need a 2nd video processor to do this, which would mean a 2nd video card, which the Mini can't really do. Maybe there is a DVI to Svideo processor somewhere, but I couldn't see one. This would be a few hundred bucks, too. Probably more worth it to save towards an HDTV to replace your old TV, this would have DVI or HDMI.