The NForce2 chipset unlocks 12.5 multipliers and lower ("IF") the CPU has a default multiplier of 12.5 or lower. You have to connect pins or cut bridges to get that 13 multiplier or higher. Also the Nforce 2 has AGP/PCI lock so no worrying about dividers or burning up a HD either. Try running 200X11.5 for starters then go to 12 multi. Also are you running dual ddr mode since you have Nforce2 chipset?
K7N2 Delta-ILSR
XP2100+ @2300MHz 200x11.5
2 X 512megs Samsung DDR 3200
Radeon 9800 Pro
Sound Blaster Audigy Gamer
2 X 80 Gig WD hard drives 7200rpm