|1700+ runs at 133Mhz fsb. 11x multiplier|
2500+ runs at 166Mhz fsb. Also 11x multiplier
A7N266 VM supports 100 and 133Mhz fsb; but not 166Mhz fsb.
As I recall, this motherboard is kinda strange concerning BIOS settings. Can you raise the fsb in BIOS?
Bottom line is that your board doesn't support 166Mhz processors. Only thing you did wrong was buy the wrong cpu.