Basically they're the same cards, Nvidia just rebadged the 8600GT to the 9500GT. Of the 2 cards i'd go with the XFX card, but they're both pretty weak cards for gaming. A better choice would be a HD4670 graphic card. You have other better choices that should be about the same price as the ones you have listed, but they may require a 400w or greater power supply. What is your power supply rated at ? Here's a couple of links that show relative performance of different graphic cards and how they perform with recently released games.
but i have a 1024x768 display and a 450W power supply.
Aren't these cards sufficient for my display as HD 4670 is little
high on price in my area?
Also What if i choose a XFX 9500GT against XFX 8600GT...
Go with Newegg, which offers great GPUs at the lowest prices.
Get a mid-high end GPU such as the 8800GT/9800GT or as bossman34 said, the 4830. All of those mid-high end cards goes for around $100-$120 on Newegg. Get that at a minimum if you want to play the latest games at decent FPS. They are leaps and bounds better than the 8600GT and 9500GT.
Don't bother going for a 8600 cuz the 8x00 series (except the 8800) all suck, and both the 8600GT and 9500GT at $100 is way overpriced for medium end cards.