Plain and simple u need to replace that card, even graphic cards that came out 3-4 years back the cheap nasty GF2 mxs for 25 quid came with a S-video output!
And you can get GF4mx/Radeon 7000 AGP or FX5200 PCI cards for about £29.99-£39.99 with an S-video out, be a lot better then using adaptors and other box devices.