the problem you face is hdmi is digital and s-video and scart are analog, so to go from hdmi to scart or s-video requires a converter box, not just a cable. there are dvi to s-video cables or scart i see on the net, but i have never tried them, and i read you need to be careful that some s-video connections have different amounts of pins, and there are two kinds of scart connections!
EDIT: I also see there are vga to s-video cables, but again there dosent seem to one cable fixes all, maybe you could check with the graphics card manufacturers website to see if they have a dongle for your card?