Daniel Christlein asked about textbooks on composition. Unfortunately
a "how-to" book on composition will often yeild rather "canned" results.
I do have a few recommendations for points of departure.
There is a very good Theory book called "Tonal Harmony" by Koskal and Payne
that has a workbook with many chances to exercise the harmonic material
presented in the text. That is a good nuts and bolts way to approach
writing tonal music.
Another great source for inspiration is Paul Hindemith. His Harmony books
offer great suggestions about where to begin when writing music. His book
Composer's World is one of the finest books I have ever read about
composition, though it doesn't say a word about how to proceed.
I hope this helps. Really the best way to go about writing music is to
study with a composer or a composition teacher. It makes the whole process
much quicker to have your questions answered directly by someone with
experience.
Elaine Fine
(returned to the list after a few years away--and now studying composition!)