I'm not aware of any programs that use that exact algorithm...however, there are much much much more secure ways of encoding your data, that's what computers do well (they also crack them well too).
For you, I would recommend just password-protecting your Word files...Obviously I don't know what version you run, but I will assume Office 2000. When you save your document, click on the Tools button at the top right of the save dialog and select "general options". and then enter a password under the "password to open" section.
Does anyone know of a program that I could use for stuff that can take the text I type, and then put it in a code like this:
A = Z
B = Y
C = X
D = W
E = V
F = U
G = T
H = S
I = R
J = Q
K = P
L = O
M = N
N = M
O = L
P = K
Q = J
R = I
S = H
T = G
U = F
V = E
W = D
X = C
Y = B
Z = A
It would be good for posting in journals and stuff so that only the people you want to read it can, and for other usesless crap.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic