Ok a quick lesson in how core 2 systems work since I'm not working today and my coffee came out particularly well.
The OP has an e6400, with a FSB of 266 or 1066 effective. That means he really only needs ddr2 533 to run 1:1 with his FSB the way his system is now. He would need to overclock his computer to at least 2664ghz before his ram becomes a problem. At 2664ghz ddr2 667 will also be 1:1 with the FSB.
So you see his ram is plenty fast even for an overclock, just throwing faster ram with higher bandwidth will do nothing for his performance.
I would overclock that chip to around 2.8ghz and lower the memory timings a tad if not stable and your good to go until a full system upgrade.
Thanks for your input guys (malmental and Sportsfanboy) I cannot read the other guy's posts maybe it was deleted . I am just gonna ask one more thing if you guys do not mind... I am a big noob when it come to CPU overclocking never done it before and I would rather not change my cpu cooler, I checked my temperatures on everest and it showed 45 C whilst multitasking is that too hot to consider overclocking? Also is there a noob starting guide for someone to do such a thing? Thanks