Complex sentence: The new Office Open XML format will be built into the next version of Office for the Mac, Office 2008, but it is also supported on Office 2004 with the help of a free conversion tool available from Microsoft.
Split into simpler sentences: The new Office Open XML format will be built into the next version of Office for Mac (Office 2008). However, it is also supported on Office 2004 with the help of a free conversion tool available from Microsoft.