oh you have a64, then use dividers. if your ram is DDR400 and you want a 2.5ghz overclock on that, try playing with different dividers (cant be bothered to work out the ideal one) and push the HTT to like 280 and to be safe set the Cpu VCOre to 1.575 v. check what your ram MHZ is with cpuz (google it if u haven't got it!) and keep adjusting your divider until your ram is as close to 200mhz as you can make it, without it rebooting your comp.
oh ya, with that a8v, its nice and OC safe, ie, if it fails it will often let you boot up. seems that way anyway... goodluck!
edit:also, depending on how low your ram MHZ goes, you can lower the timings on it as well, for better performance (check my sig - i used divider to get my ram at 170mhz instead of 200, and dropped cas latency to 2, for example)