FSB overclocking on the old Athlon 64 X2s isn't exactly rocket science, but it isn't very simple to explain either. Your best bet is to google around for FSB overclocking. I did it awhile back (64 X2 5600+), and honestly don't remember my settings.
The basic idea is you have to raise the FSB in the BIOS, boot, benchmark, and repeat until you crash. Then you can try increasing memory voltage, or changing the memory multiplier and see if that works. If it doesn't you reset those and try changing the core voltage. Or the HT voltage. Or the HT multiplier. You have to approach it with the scientific method and eliminate variables one at a time.
It takes a long time and a lot of different voltages/multipliers/FSB combinations to find the best stable setting. You could end up with something ridiculous like a 300MHz FSB with a 11x CPU multiplier and memory set to 667 Mhz for a 3.3Ghz CPU clock and 1000Mhz memclock.
It can take many hours to get a good stable overclock with tightly tuned memory.