Diagonal Lines in SD 4:3 Mode

When watching SD in 4:3 mode from my MCPC some channels have very steep diagonal lines about 1/2" apart. No problems with HD or DVD's this only appears in SD content so I believe it is related to my SD signal. I have searched the forums and google for diagional lines with no relevent results. Does anyone know what is the cause of these lines and how can I eliminate or minimize them?

Thanks in advance!

My setup:

Media Center PC custom built
Silver nMEDIAPC Media Center HTPC 200SA,
AMD MT34,
Zalman CNPS7000B-ALCU,
Hauppauge WinTV-PVR 500,
ATI HDWonder,
PNY 1Gb PC3200 DDR,
ENERMAX Liberty ELT400AWT,
Thermaltake Media Lab Black,
WD 400Gb SATA HD,
Wireless B
Samsung HLS 6187, connected via VGA, calibrated with MCE2005
Sony stereo
Time Warner Expanded Cable (Pre-split at least 5 times by condo builder)
OTA HD

Here are pictures of the situation. I think it is called "beats" and has to due with singnals occuring on a harmonic of the channel. It does not occur as bad when the cable is plugged directly into the TV. Also this happens on many channels, but not all and is not concentrated arround any range of channels.

Picture 1
Picture 2