I wouldn't really recommend the s-video cable. Seeing as s-video is an analog signal and not digital its not going to display the picture in any kind of good quality no matter what resolution. Simply put its not the ideal connection for your HDTV. Your best bet would be to purchase a card that has the capability to output in HDMI, DVI, or VGA. The price for a card is really not that much and if you want HD quality then a nice card is necessary. I don't know what kind of port you are running but it possibly a VGA port. Newegg normally has great deals on video card that meet your budget here
On a side note the quality for connections on a TV is this (from lowest to highest):Coaxial (audio and video on same wire)
Composite (audio and video is separated with 3 different cables)
S-video (just video colors seperated even more with no audio)
(Just video where it separates the video colors even more)VGA
(Most HDTVs are set up to do this from a computer. Video only)DVI (only Video)
(also incorporates audio in Dolby Digital on the same plug)
to newegg for the cables.