Jabo 1.5 Question

Why is it that every time I play games with PJ64 or 1964 with Jabos D3D7 1.5 (supposedly the best graphic plugin) the games generally run fine, but the graphics are "boxy" unless I select RGB emulation, which looks great, but the game then runs really jerky.
Is there a way to fix this or is there a better plugin to use? Im running a P3 700 w/ 256mb SDRAM and a stock graphics card.

Thanks All,

DrewDown