I just removed all the standard Ubuntu 8.04 OpenOffice 2.4.1 packages and installed Openoffice from Openoffice.org’s download area by following the howto here.
After going into Tools ==> Options ==> Language Settings ==> Languages and setting everything to English (Australian) I gave a document a test to see if spell checking was working and it failed to underline or even check the spelling.
Download and Install the Australian Dictionary from here http://extensions.services.openoffice.org/project/AustralianDictionary
When you do the download Firefox seems to recognize that it has to be opened in OpenOffice and the Install is automatic.
Once it’s installed and your set to “English (Australian)” you get the squiggly lines under your text as you would expect.