There is no 9600XT with or without DDR. It comes in one flavor.
In the 9600 family there is the:
9600SE (marketing product; stay away from it)
9600 (same as the Pro, with slower ram)
9600Pro
The above products are all based on the RV350 ATI GPU, which is a low cost version of the R350 (9800 family) (half the number of pipelines is the basic diference).
The R350 is a .15 micron part, while the RV series are .13 micron parts.
9600XT is based on the RV360 GPU. While having the same basic specs as the RV350, the big difference is this is the first chip to successfully make use of low-k dielectric technology, which allows for higher clocks and significantly less power consumption (i.e. much less heat).
Some of the third party suppliers of ATI products are putting faster RAM on their version of the 9600XT, and raising the clocks on the RAM for better performance.
The GPU on the 9600XT can overclock very well (some sites have reported successful clocks up to 625Mhz).