Headliner replacement

I've been following Mike Spera's posts about refurbishing the interior of
his Cherokee and have some questions about replaceing a headliner.

The headliner in our Aztec has several zippers, some of which don't work and
a couple of which are ripped out causeing air leaks and cold drafts. During
our annual next month we plan on removeing the plastic window trim pieces
for some paint and polish and as long as we have them out, I'm wondering how
hard it is to replace the headliner. For just a few hundred bucks we can
get a new one from Airtex that would definately fix the drafts and dress up
the interior. It would also give us a good reason to snoop underneith it
and inspect the cables, pulleys, and air vents more closely.

Has anybody tackled it? What's involved? How many hours?

Thanks again,

Jim