DDR-SDRAM is DDR RAM.
Plus you must remember, SDRAM runs very slowly, at much slower speeds then DDR, and even if you could use it, it would make your PC much slower, becasue the whole Front Side Bus (FSB) would slow down to the speed of the SDRAM, probably 100 or 133MHz. To give you some comparison, a P4 2.4C/2.8C/3.0C, runs at 800MHz FSB (Thats the model "C" p4s). The front side bus would go from 800MHz to 100 or 133MHz.