Gbaby...
As everyone is telling you, it would not be worth the money to upgrade your 3000/333 to a 3200/400. I doubt that you could even tell the difference if you overclocked the fsb up to 400Mhz. As for the memory, your board should be a dual channel, and removing the third dimm will allow you to run in that mode, but I doubt you would notice anything with this change.
Now if you were to remove the dimm, up the fsb to 400 and make sure your memory timings are as low as possible, you may notice your fps goes up in games, but I still don't think you would notice a difference on your desktop.
I just finished OC'g my sons 2600+ to 2.2Ghz and upgraded the memory to 1GB (512x2) and if when he plays COD, the FPS increased about 5-8fps. Minimal, but that is noticable for him. As for desktop performance, nothing...
Hope this helps.