you mean like, polygons jumping around? the only thing you can do is just put the resolution lower...it's caused by the PSX not having subpixel accuracy, therefore when something moves 1 pixel at 320x240 (native res) it looks normal, but when you are running at 640x480 or 1280x960 or whatever, it has to jump 2 to 3 times the original distance and looks bizarre.
so play at a low res (i.e. 640x480) or just learn to live with it
ummm....unless you are talking about something else? perhaps like textures in the ground or on a character flickering? in that case, change/turn off texture filtering.