Roof Leakage?
 

My daily driver is a 98 Grand Prix GTP four door, with the moon roof option. Now the cover that slides under the moon roof window has been stuck in the open position, so I cannot slide it closed at all. Now once and a while after rain storms, there can be a large puddle on the front passenger side floor. Also some water can drip out of the open moon roof and overhead lights panel on the roof. Could a drain be clogged, and if so where can I locate the drain? Is the stuck cover and the water seepage connected at all?

I would suspect a clogged drain. You should be able to see it with the roof open. Try fishing some fine wire down the drain.