I have never done what you are trying, but I would just copy the iTunes Music (or iTunes Media) folder from the PC to the Mac and let iTunes re-index it all. If you don't let iTunes consolidate all of your music into the one folder on your PC, you'll have to copy all the files over to the Mac and let iTunes find them all.
You may also get a better response by posting the question in one of the [iTunes forums|http://discussions.apple.com/category.jspa?categoryID=149].
In the iTunes Forum, I searched for "import Windows itunes" and found these two (among others):
http://discussions.apple.com/thread.jspa?threadID=2005791 and
http://discussions.apple.com/thread.jspa?threadID=1956560.
The second one has lots of links to how-tos.