The ETD initiative provides you a unique opportunity to learn more about publishing. The skills acquired in doing an ETD will serve you well as you continue to produce works of scholarship, more so if you choose to remain in higher education. We encourage you to start learning about publishing issues in the process of preparing/submitting your ETD.
By submitting your ETD to the Montana State University Library, you are embarking on a form of publication for your thesis/dissertation: you are making it available and accessible to a wider range of readers than could or would gain access were it to be deposited in bound form in the University Library in the traditional way. The fact that the work is thus being made available is relevant to the decision that a book or journal publisher might later make about publishing or not publishing your work.
First, the degree of availability matters. If you have chosen to restrict access, this will matter little to the publisher. But if you have allowed world-wide accessibility, then a publisher may well be concerned.
With respect to journals, some insist rigorously on first publication and might well interpret world-wide availability on the Web as tantamount to prior publication. They would therefore reject your submitted article for that reason. To be totally sure about this you would need to identify in advance the journals to which you might wish later to submit your article and discover their position on this question. It is not possible to generalize about which journals might adopt which policy. Many journals with an excess inflow of papers might well consider the prior availability of your paper as reason to pass over it and allocate their scarce space to another less widely available paper. Again it would be wise to inquire as to the practice of those journals in your field. Of course in many cases what you submit to a journal will be considerably different from the material in your dissertation.
The second issue is an economic one and more relevant to book publication than to journal publication. Many academic books have very small potential sales and are at best economically marginal. Anything that means some part of the total potential audience will not buy the book but will obtain the text in some other way (e.g. from the Montana State University Electronic Library) reduces the sale and makes it more likely that the publisher will assess the likely sales and conclude that the work just cannot be published economically.
On the other hand, some people will argue that availability on the Web, because people will neither read a full book on screen nor print the whole thing out, acts more like marketing for the work and does not eat into sales of the book itself. Indeed there is some evidence that sales of the book may even be enhanced. These issues are still in the very early exploratory phase and nothing certain can yet be said. It would be my advice to take the cautious view and assume that the publisher with whom you would like to publish your book may base his or her policy on the pessimistic rather than the optimistic view.
In any case, it is the extremely rare dissertation that is published as a book without major revisions. Most authors spend several years rewriting and developing the ideas and argument in their dissertation. The more your book manuscript differs from the dissertation, the less it will matter to the publisher whether or not the original dissertation is available electronically. Where the dividing line is at which the original dissertation becomes irrelevant is a matter of judgment for each individual publisher, but it is probably wise to assume that by making your dissertation widely available electronically you are somewhat raising the threshold of acceptance for that later book manuscript.
These issues are relatively new; nothing certain can yet be said. You may want to take the cautious view and assume that the publisher with whom you would like to publish your book will be concerned if your work is readily available through the Internet. You might then opt for restricted access to your dissertation at first until you have identified a potential publisher and determined the publisher’s policy regarding ETDs. The publisher may have no problem with your making the thesis/dissertation available immediately through the Internet.