OK, I thought you might of meant that but wasn't sure... RCA(what you're talking about) is actually one of the lowest qualities of input you can use!
As ardy89 said, play with the sharpness and other settings on youre computer. IT's never going to be too clear because of the resolution differences. The computer has to cut the res down a good bit to make it work on the TV at all... The lower the res is on your computer, the better it'll look on the TV.
Desktop: Athlon 64 3700, 1024M RAM, GF 6200 TC 256M, 2x 80G, 2x DVD-RW
Laptop: Sempron 2800, 512M RAM, Unichrome, 60G, DVD-RW
Macintosh:G4 1.33GHz, 512M RAM, Radeon 9200 32M, 40G, DVD/CDRW
They get me from 0 to 1...