I do not have an Axim, so I am not so familiar with the updates that are available for the x51. Updates for the x51 can be found on Dell's website:
Drivers & Downloads
I can only point you to the website, but really cannot provide much advise regarding the updates there. Reviewing the x51 forum and posting a question there might yield better information about specific updates you might need to install.
What you describe sounds like a conflict with your Zondervan application. You could try deleting the application and then see if you still have such problems. If the problems go away, then it's probably safe to assume that the Zondervan application is what caused the issue.
It sounds like the Zondervan application may require quite a bit of memory to run. Have you installed the application to a memory card or to main memory? There are other bible applications that you could try which might work better.