Cool! If you can do basic Java programming, then yes, OpenMark is a good way to make really interesting online questions.
The way we (at the OU) get the results for OpenMark tests to the Moodle gradebook comprises two parts.
First, there is a basic XML format that you can import into the Moodle gradebook. OpenMark can export grades in this format. Doing the export should be one of the options when you are looking at the reports on a test. That lets you transfer grades manually, by doing the export from Om, then the import into Moodle. Simple, and possibly sufficient.
Second, we build a simple custom Moodle module, called externalquiz. That module makes it easy to add an OpenMark quiz to a Moodle course (it automatically adds a link to the course page and a column in the gradebook). It also automated importing the grades from Om - it does an import once per day, in the middle of the night.
That externalquiz module was cobbled together in a bit of a hurry, and so in not the best code we have ever written at the OU, and so we have never shared it. We are about to convert it to work with Moodle 2.0, and hopefully we can clean the code up at the same time, in which case we might share it.
Anyway, in the first instance, I would suggest you use the manual process, so you can see exactly what is happening, and check that the import has transferred the grades accurately.
