At 480i, there's really only minimal difference in the quality of signal you can deliver between S-Video and Component (composite will look terrible, of course). I have an RGB to S-Video adapter I built that actually gives outputs darn near indistinguishable from an arcade monitor on most arcade video signals. The biggest thing your component setup does is eliminate the scaler chain that the TV output encoder uses. These scalers usually a) suck, and b) attempt to underscan the image for you, resulting in even less resolution than your TV is capable of actually being used.
Some TV output encoders are somewhat smart and will disable their scalers if told to do so by software and fed a compatible signal, only interlacing the output as required. Try setting your desktop res to 640x480 at 60Hz (VESA VGA standard, pretty much compatible with ATSC 480p) and disabling underscan (or set full overscan) in the TV output settings. Depending on several factors, you may only be interlacing the output, rather than scaling it, which doesn't really affect visual quality of static images. Failing that, either find yourself a component dongle if your TV supports it (it's stupid that you should have to resort to this, but it's the way PC video cards are made) or find a video card with TV out that doesn't suck (good. luck.).