The X2 3800+ was my favorite processor until the Intel Conroe came around. I understand that not alot of people can afford a new processor, because to upgrade now means you have to get a while new motherboard, DDR2, AND the new processor.
I was able to overclock the 3800+ a good bit (like a 4400+ equivilant), but your mileage may vary depending on your motherboard. Basically if you decrease your Hyper-Transport from X5 to X4 then you can throttle up the FSB. The goal is to try and keep the processor frequency as close to 1000Mhz as you possibly can.
by default, the FSB is 200, and with an X5 multiplier the HT bus is 1000Mhz. Decrease to X4, and you should in theory be able to push the FSB up to 250 (assuming your RAM can handle it). Once you hit a limit, then you have to experiment with voltage, memory timings, etc.
When overclocking, the computer eventually becomes unstable, so I really don’t recommend overclocking over 10%. If you stay within a 10% overclock, it should be pretty stable.
If you’re overclocking to increase your gaming performance, then don’t bother with overclocking and upgrade your onboard video with an nVidia 7600, ATI X1600, or another cheap (but powerful) video card.