Since you've bought a K7N2, just don't be alarmed when the voltage adjustment doesn't work. It will work the first time but many users of K7N2 have experienced that in order to change the core voltage (subsequent to first adjustment), you would have to set it at "H/W default" and reboot then change the voltage. I have experienced this also as my wife's K7N2-L was unstable when overclocked w/ 1.625 voltage. I tried numerous times to increase the voltage but it never happened until one day I read numerous posts regarding this problem on another forum (MSI's website or nforcershq.com, maybe amdmb.com).
Also, any adjustment to the dimm voltage will not work although it provides an option for it from 2.5~2.7: I also experienced this. Although K7N2 does not have all the features and overclocking options of other brands, it's a very stable board and performs quite well (10.5x200 w/ a XP1800+), and best of all, it was $30 cheaper than my Abit NF7-S. I've heard that an updated bios will be released very soon. Hopefully, the problems I've mentioned will be addressed.