Well if there's 12 characters consisting of only letters (as opposed to numerical or other characters), then there is only 26^12 (95,428,956,661,682,176) different possible combinations. If you count upper and lower case separately, there is 52^12 (390,877,006,486,250,192,896) different possible combinations.
It would take about a year (according to my math) to crack the password if it's case insensitive and 3,024,025,746 (rounding up) were tried every second.
It would require 12,386,409,454,632 tries per second to crack the mixed case (and case sensitive) password in a year.
...but then again, it you
could get it on the first try
How I figured this (if anyone's interested):
(((26^12)/(24*365.242199))/60)/60
(((Possible Characters^Pass Length)/(Hours in day*avg Days in year))/Minutes per Hour)/Seconds per Minute