if it is a store brought pc then you cant overclock, if it is custom then you should get about a 600MHz overclock out of your 3800 with stock cooler
but before this happens, we need to know if your memory is good, if you have value memory then probably the most you can overclock the memory is around 8-10 MHz
see if you can lower the speed of the memory then increase the FSB, when suing value memory, you want to be as close to stock memory speeds as possible