Yes, longer ago.
But if you want a more helpful answer you might post a bit more information.
What I know are that some differences for EJB's. (e.g. locking behaviour).
If you use standard J2EE you might have no big problems.
please let me know what info would you require.
i am using ejb2.
oracle db 10.2
HP-UX 11.23 ia64
your informations are a bit sparse.
I would prefere a Java 1.6 (latest patch).
HP might be a problem, you should look to http://docs.hp.com/en/HPUXJAVAPATCHES/index.html#whathpux
For oracle the version should be (more or less) transparent, but the ojdbc6 driver looks best.
Other migration stuff depends on your application.
My one is mostly with EJB's. After migration the application run faster because of the EJB3 persistence.
Here lot of database roundtrips are not necessary if you pay attention to the new behaviour.
So what kind of application do you have to migrate?