This seems to be a pretty big topic of conversation with companies that do not want to migrate VB 3-6 applications to .NET. There is a company called Diamon Edge that provides a set of tools to do most of the conversion work for you.
VB Converter add-in is specifically designed for organizations wanting to convert entire VB applications to Java and SWT in order to take advantage of Eclipse's Rich Client Platform (RCP) and IBM's Lotus Expeditor (previously known as WebSphere Everyplace Deployment).
As you can see from the product page, the VB to Java converter has a lot of features right out of the box. It would be interesting to hear from any developers or companies who have used this product and get some first hand experience in converting a relatively large application over to Java and more specifically Lotus Expeditor.