1) The Asus P5RD2-VM motherboard has a PCI Express x16 slot.
The Nvidia 9600GT uses a PCI Express x16 slot.
2) The PCI Express version used on the Nvidia 9600GT is PCI Express 2.0
The PCI Express technology used on the Asus P5RD2-VM motherboard is PCI Express 1.1
The motherboard chipset used on the Asus P5RD2-VM shows us this.
The motherboard chipset is an ATI RD480. (Before AMD bought ATI out)
The ATI RD480 chipset came out September 27, 2005.http://en.wikipedia.org/wiki/Comparison_of_ATI_chipsets#Comparison_of_Northbridges
Scroll down until you come to > RD480 in the left column, then read across.
The PCI Express technology started under another name, then was changed to PCI Express.
The first version was PCI Express 1.0
Then PCI Express 1.1
In 2007 (January 15) the PCI Express 2.0 technology was brought out.
The PCI Express 2.0 technology is Backward Compatible with the PCI Express 1.1 technology.
(With PCI Express 1.0 also, but it depends on the graphics card being used)
In otherwords, a graphics card that has been based upon the PCI Express 2.0 technology, will work on a motherboard based on the PCI Express 1.1 technology.
You won't get the full capability of the PCI Express 2.0 graphics card.
Will you notice?
[ If I had my choice I would run an Nvidia 9800GT instead.
Depends on the price, and availability of the 9600GT I would assume, though.
You may also need a more powerful Power supply.
Example, not advertising,http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=6391081&CatId=3670