KK vs. AA

[avisco01]

Just curious...when you hold KK at a 9 handed table, what are the odds that someone has AA? What I mean is, for all the times you are dealt KK, how many times will you be up against AA? I thought I read somewhere (don't remember where) that for every 25 times you hold KK, you will be up against AA once, thus its roughly 25:1. Is this true, and if so, how is this figured? As the number of players decreases, all the way down to heads up, how less likely is it for this horrible scenario to take place? Any help would be greatly appreciated, thanks.