X1650 to 8600GTS

would you say this is a good upgrade? ATi Radeon X1650 (512mb) to a nVidia 8600GTS (512mb)
ive only done RAM upgrades before, so does anyone have any guides that they used which you could reccomend to me?
also, the only place ive seen sell one of these for a reasonable price is eBay. anyone know a british place that sells a 512mb version of the 8600GTS for about
ive only done RAM upgrades before, so does anyone have any guides that they used which you could reccomend to me?
also, the only place ive seen sell one of these for a reasonable price is eBay. anyone know a british place that sells a 512mb version of the 8600GTS for about