OpenOffice.org Tips and Tricks Part II - page 2
Importing MS Office Custom DictionaryDo you find yourself regularly having to save your OOo files to the MS counterpart? Well you will probably always have to, that is until you can convince your IT department and colleagues to dump Microsoft and go open-source. While the debate continues, though, you can make it a bit easier on yourself. Instead of having to do a Save As after finishing a document, you can set OOo to always automatically save in the MS (or any other) format you choose.
When you have OOo open, click Tools -- Options, expand the Load/Save category, and select General. Then in the Default File Format section, choose the document type you want to set and select the format you desire, as seen in Figure 4.