How about DOCX? (the Vista and up default for Word)
I have a plug in for XP that works.
Pretty sure you can open them with OpenOffice, though I haven't gotten any and had set my work computer to save as the old formats.
By the way, .docx and the like (.pptx, etc) have nothing to do with the version of Windows, but rather the version of Office. It's an XML-based format that Microsoft adopted starting with Office 2007, similar to what OpenOffice was already using. It is also an open, ISO/IEC certified standard.
