You could also consider using Jython for this as you can, effectively, script Java classes together.

However, I wonder why you cannot simply use a web interface and make use of the excellent templating tools already available to you? This way the target user needs only a web browser and login and reduces any complexities of installing and maintaining revisions of software at each and every client.

Seeing as you admit there is little or no Java experience, attempting any form of Swing is going to be a very big job. Writing Swing is fairly easy but writing Swing well and stably (is that a word?) isn't. Believe me I know ;P.

As mentioned above, you could make a middleware tier and simply query it via SOAP and abstract your data management even further if you found it necessary to. This would tie in nicely either with a GUI or web-front end.

HTH