Found a link explaining how to enable saving as a WordPerfect document in MS Word 2003, but it seems that the format is not supported by latter versions of Office/Word due to security concerns.
But if WordPerfect supports RTF (you don't specify which version of Word or WP you are using) you could use one of these scripts written by Rob van der Woude to automate batch converting documents from Word into RTF and then opening them in WP.
Hope this helps somewhat...