If you are getting an error saying you don't have Pixel Shader version x, that usually means your graphics hardware is not capable of playing the game. If you have a desktop computer, buy a new video card. If you have a laptop, you won't be able to upgrade the graphics and you will have to get a new laptop to play.
Pixel Shader 2.0 is hardware, not software. You cannot download hardware. If you have a laptop, then you will most likely have to buy a new laptop. Very few laptops allow you to upgrade the video card, those that do are usually costs $1,500+. I am assuming you have a laptop since you posted in the "Handheld Gaming" sub-forum even though playing games on laptop is not considered handheld.
The fact that whatever laptop you have does not have Pixel Shader 2.0 means you have an old laptop. Laptops with video card that supports Pixel Shader 2.0 were released in 2003 beginning with the Mobility Radeon 9600 and the nVidia GeForce Go 5200. Intel released their GMA 900 (found in the Intel 910G, 915G, and 915Gx chipsets) in 2004 which is their 1st integrated graphic core with Pixel Shader 2.0 support.