Microsoft's Office 2007 for Windows saves documents in a format that's incompatible the company's Mac Office application.

By default, Office 2007 saves documents in what the company calls "Microsoft Office Open XML". The new format applies across Word, Excel and PowerPoint applications on PCs using Office 2007. The formats are specifically termed: docx, xlsx and pptx.

In a momentary throwback to the old days of incompatibility, documents saved in the new formats can't yet be opened on a Mac.

Office 2003 for Windows users can download a compatibility pack which makes it possible to open Office 2007 documents.

However, the company's Mac Business Unit hasn't yet delivered similar software for existing Mac installations of Office. It has promised to ship them, but hasn't yet committed to a specific date for this.

There is some hope — and a hint that Mac users may not have to wait too long to enjoy cross-platform parity with Windows: Novell has promised it will release code that supports the new Office 2007 formats to the open source developers of its alternative (and free) productivity suite, OpenOffice.org. This support is scheduled to debut "by the end of January". Novell will also release translation software to help documents created in either suite to be opened in the other.