Word 2007 and later can all quite happily read Word 97-2003 files without doing any conversion. The real issue, though, as Andrew pointed out, is that blogs typically work with the HTML format, not Word's .doc or .docx formats. And, while Word 97 and later can all save to the HTML format, the HTML code they produce is truly horrible.

If you're lucky, the WYSIWYG editor for the blog will allow you to simply copy & paste formatted content from Word into the editor; otherwise you might try saving the document in HTML format, then importing that. The worse-case scenario is that you might have to copy & paste the Word content as plain text, then reformat in the WYSIWYG editor.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]