Nice intro, a couple of add ons to anyone interested. hidden is right on track with the letter frequency gig, first step in breaking a simple code like the example. Frequency of letters in english from highest are as follows:

E T N O R I A S (remembere the word SENORITA)

Easier to spot than the tri graph info like ING are repeated letters, or doubles like TT in letter, or LL in yellow. Very easy to pick out if a simple cipher like the example is being used.

Hope this helps to demonstrate how telling and important a letter frequency count can be, not only to breaking a code but also in determining it's complexity as well.