Yes, you'll be able to use DDR RAM with it.
But only the PC1600 if you don't overclock the FSB. And PC1600 is terrible in performance. PC133 SDR RAM is better.
However, if you want to run PC2100, then you'll have to overclock by 33%. Or you can try and manipulate the multiplier, but that requires you to unlock it. Some T-birds I heard are already unlocked though.