When microsoft released office 2007 it used OOXML formats such as XLSX and DOCX, which limited POIs capabilities. The earlier versions of POI used OLE 2 Compound Document format, and now you can easily read or write excel, doc(97-2007).
The latest release POI 3.5 final came out in 28-September-09 and I am very eager to use it for my project and I swear u will be eager too.