I do not think that you will find a tool that does automatic merging between a Word document and a LaTeX document.
To at least highlight the differences between your two versions you could take two filters that cut away the formatting in both versions and then use the diff-tool to compare the content (i.e., the resulting plain text files). Then you can do the merging by hand.
On *nix it is as simple as this:
antiword cv.doc > cv-doc.txt
detex cv.tex > cv-tex.txt
diff -u cv-tex.txt cv-doc.txt
(provided you have the antiword package and detex, which would usually come with your tex distribution)
If you want colors in the diff, try this post.