Hey Stain,
My take on your question: Either you want to use your old SD-Ram- and go with a KT133A mobo, or you want a modern system & you do not have any DDR yet............but you want to get some in the future.
My Answer: Do not buy anything until you are ready or totally need to buy everything..........& buy everything at one/same time. Reason: of all the dual memory mobo's, all their performance sucks even with DDR...........the ECS K75SA is the only dual memory mobo that has decent performance, but this mobo is made with the worst production value of any mobo that I have seen! You have a very good chance if you buy this mobo, that it will be DOA.
Again, my advice: if you are going cheap, buy a KT133A based mobo, like the MSI K7T Turbo 2($65 from newegg.com). Or better yet, keep your old system & buy your new system all at the same time, saving you money & giving you even better performance & future upgrading options. Good Luck
Peace Out...................tile
god knows your entire system setup & he would answer your questions if he could just stop laughing