I think your only option will be an RF Modulator, and that is also going to affect your card choice.
Since you're planning to upgrade to an LCD in the future, you're going to want a card with DVI out at that time. I don't think there are many cards that offer both DVI and standard composite (yellow port) video out.
If the budget is tight, my suggestion is to get a real cheap used card with composite video out and an RF Modulator. The image quality using this setup is the poorest of all the connections (straight Composite with no modulator, VGA, S-Video, Component, DVI), but it'll get you a playable image on the screen with that old TV.