I ran into the same problem when importing several blogs from Movable Type into WordPress 2.5. The posts display on the main page of the blog as if they’re published, but they don’t display as individual posts (permalinks don’t work). This only occurs in IE 6 and 7.
In the “Manage Posts” section the imported posts don’t display as published or unpublished. To make them display in IE 6 and 7 you have to go into each entry and hit publish even though the post is technically published. What 3eamus and I are looking for is a way to batch publish entries so that we don’t have to publish thousands of posts one by one.