do you need windows vista in order to run Geforce 9500 GT video card??
No it should run fine in XP, Vista and Windows 7 as well as Linux and Mac OS X. Probably would work under Windows ME and 98 too if you could find driver support.
All you have to do is go to www.nvidia.com and follow the download drivers links to whatever operating system you have.
do you need windows vista in order to run Geforce 9500 GT video card??
No you do not Vista in order to run a 9500gt. You do need a proper PCIe x16 port on your MB of course and then you need to update the Nvidia driver for your OS which is Vista. If you do not utilize the driver your motherboard will use the onboard graphics, hence Windows Aero will not work well. Unless you have the GPU properly connected and have the proper Nvidia driver for Vista you wont be able to play newer games as well.
That graphics card can work with most operating systems including Apples OSX's. So as long as you have the specified Nvidia driver, then you can run that 9500gt with any OS you like sans Windows Me.