How did you connect the VGA card to your TV? Do you use a TV output? Or Do you have an ArcadeVGA? Or are you using PowerStrip or a software to force a 15khz output from the VGA card?
A TV can not display 640x480 . Except if it is interlaced and in that case it is not really readable on the screen.
If in your previous cab you were under windows too and it was readable, it is may be becauce you were using PowerStrip in a non-interlaced mode (certains version of powerstrip have a 640x480 mode non interlaced (in fact it only display one row on two)). In that windows is not readable, the image is very stable, and it is very good while playing game.
if you are using an ArcadeVGA , try a resolution under 640x480 ( ex: 640x288)
It is just some thoughs , i hope it helps you.