Game Framerate Help

I have the Dell Inspiron 530 with the core 2 duo e7400, 6gb of ram, 1.5tb harddrive and now a radeon 5670 graphics card recently upped from a gtx 9400. This is mostly a wow computer and i honestly just want to get it to the point where i don't lag, i would of course like to pump as much as i possibly can out of this system, but trying to stay on a budget. Don't want to put too much money into something that i should just replace anyways.
This computer is mostly for wow so not too much intensity is required of it. I mostly 25 man raid so i was getting some lag spikes with the gtx 9400. I thought bringin up the graphics card would help but it just ended up being about the same. I just wonder what would be the best option to bring up my frames on this computer and stop getting lag spikes?
i debated returning the graphics card and instead getting a new mobo so i could overclock it, but i know im limited by the power supply in the computer. Any ideas would help.

WoW shouldn't take much to run. However, I know I have a dual core in my little older custom built, recently upgraded the video card. In some games, such as Battlefield BC2, I get slowdowns due to a CPU bottleneck. Could be what's happening with yours, but try turning down a few of the settings and see if that helps. I would also consider returning the 5670 as that's about a 100 dollar card. For not much more you can get a GTX 460 which is a much stronger card.

Basically, if you've got an older chip, what happens is that the card feeds more frames to the cpu than what the cpu is capable of handling. That's what's happening to me in Battlefield. The card could run full settings I think, but my cpu holds it back until I get a better one. Turn up your resolution if you monitor can go higher, because they say cpu's are not held back at higher resolution as much. The best option might be though to start saving for a newer system.

If you do look at a newer system, most of your parts are likely modern, you may be able to just get a board, chip, case and power supply, maybe ram, which is cheap enough, and start over. Maybe sell your old ram to help out on the cost.