The motherboard is designed to work with either DDR1 or DDR2, but not both. That means, as stated in the comments, the critical specification is not if the CPU supports DDR2, but if the motherboard supports the CPU. If your motherboard (model not specified in the question) supports the T9500, and the RAM socket is designed for DDR2, then the components in the motherboard facilitate communication between the T9500 and DDR2 RAM, period.
If you cannot find information online about your computer model/motherboard, an easy way to verify that you have DDR2 RAM is to look for "PC2" printed on the sticker on your RAM modules. Alternatively, Piriform has a free program called Speccy which is very useful for hardware identification.
To make things easier and answer your specific question, both the T9500 and X7900 have been sold in computers with DDR2 RAM, proving their compatibility. (IBM/Lenovo T61 and iMac Core2Extreme).