First, is this an X2 5200+ Black Edition or normal chip? Big difference in how you overclock these. If it's a BE you basically just increase the multiplier and test for stability at each bump up until you see instability, then set it to highest stable multiplier and you are done. If your chip is a standard cpu (locked upward multiplier) you need to follow the overclocking guide.
Here's the logic behind overclocking "normal" (upward mutiplier locked) AMD processors.
The first thing you do is determine your motherboard's maximum stable FSB (stock is 200), you want to see how fast the motherboard can operate before you see instability. This speed will represent the absolute limit to your overclocking potential (cpu at highest multiplier x max board fsb = highest possible overclock, note you may not reach this due to cpu limitations). To determine this limit, you have to reduce the cpu multiplier (so that instability is not caused by cpu operating considerably above its rated speed), the RAM speed ratio (again, don't want to get a false low reading from pushing memory past its rated speed), and finally the set hypertransport multiplier down (can't go over 1000 IIRC). Push up the fsb in 10-20 step increments until you fail to boot into Windows, then back it down about 5% from that point and run Prime95 in Windows for about 10 minutes to make sure the motherboard is stable at that fsb.
After you find your max board fsb you need to determine your maximum stable cpu speed. Set cpu multiplier back to stock but leave memory and hypertransport ratios low during this testing. Set cpu voltage as directed in the guide (or just see how high you can go on stock volts if you prefer). Start increasing fsb (from stock) in 5-10MHz increments, booting to Windows and running Prime95 for 5-10 minutes to confirm stability at each step. Once you start seeing errors or crashes/freezes you have maxed out your cpu speed. Drop the fsb 5% and boot into Windows, test Prime95 for 10 minutes to confirm stability.
Memory is not as important for AMD processors but can still yield small improvements in performance. The main thing is running a 1T command rate if possible, that will actually have a measureable impact on performance. You can try to fine tune memory speed if you like.
One final caution: the voltages mentioned in this article are outdated. They are refering to voltages used for the older generation of equipment (Socket 754/939 chips and DDR memory, both of which use higher voltages than current AM2/DDR2 equipment).