OpenOffice.org File Format Compatibility
Is OpenOffice.org compatible with MS Office and StarOffice file formats?
Yes, OpenOffice.org uses the same standardized OpenDocument (ODF) file formats as StarOffice. The ODF files can be used with many other programs on many platforms.
In general, Microsoft Office file formats can be read and saved by OOo. OpenOffice.org 3 can open the new OOXML formats by Microsoft, but will not save to that formats.
Nevertheless, the compatibility is not total. There are Microsoft Office features, such as the old equation fields (not to be confused with the equation objects), which are not read at all by OpenOffice.org.