Where might I find information of digital design, particularly of a 1
of 4 decoder? Also, information about SOP and POS equations would also
be of use to me in deciphering decoders and the digital design
process.

To implement a 1 of 4 decoder you need to understand what a finite
state machine is;

http://en.wikipedia.org/wiki/Finite_state_machine

There are a plethoria of lecture notes on the internet concerning
digital logic design - see the computer science section from this
link;

http://staff.southwest.tn.edu/kfoster/links_4.htm

But not very much background explanation. If you can decipher lecture
notes (or at least get a feel for what is involved) this is a pretty
good link;

http://www.csee.usf.edu/~maurer/logic/

But there is nothing (at least that I can find yet) that shows the
nitty gritty of all the steps of going from state machines to
equations to logic circuits in a thorough manner. Once you understand
that doing the reverse or "deciphering decoders" is straightforward
(if that is what you meant).

I recommend getting from interlibrary loan the book
 	
"Logic Circuit Design" by Alan Shaw

to see if this is suitable to your needs, before you buy, as like all
college textbooks it is pricey.

Though I have not read it, a similar and potentially less expensive
book (used) would be "Digital Logic Circuit Analysis and Design" by
Victor Nelson.

I recommend search term: digital Logic circuit design; finite state
machine; boolean algebra; karnaugh maps.

The wikipedia articles are succinct and probably better than what is
readily available on the internet.

That's pretty much the nickel (or free) tour from the google answers peanut gallery.

I found these sites very good, and I went to the library and checked
out the books that you recommended. I have some hope that designing a
decoder isn't hopeless. Thanks!