I'm doing the "skull" quest for Lothar. I got to TNO's tomb and got all the keys. When the portal opened, I went through. The next area loaded, but the game crashed. I am using all the mods from the gog mod guide and running Windows 7. Any help would be appreciated.

Unfortunately the game crashes sometimes. Check these suggestions, they might work for you:
http://www.gog.com/forum/planescape_torment/crash_when_trying_to_leave_lothars_building

Thanks for the reply, but that is not the problem I have.

When I exit the tomb, the next area (the Drowned Nations place) loads, and me and my party are standing there, doing the idle animations. I can still mouse over the time and menu buttons, but the second I try to move or open a menu, the game stops working. I have tried pretty much every solution 3 hours of Googling suggested, but I am still at a loss.

Gah, this is nasty. Probably there's an inconsistence in your savegame. I'd suggest rolling back to an older save, even though you have to play some parts again.

I went back to right before I accepted the quest, but it still crashed when I reached that part. This is getting pretty frustrating. Thanks for the response though.

I discovered a solution! I'll leave it here in case anybody has this issue in the future.

I went into the tomb, and then saved and quit. I then went to my cache folder and deleted ONLY the file pertaining to the Drowned Nations area (AR1700.BIF). When I went back into the area, my game worked. Thanks to the people that commented. Hopefully it's smooth sailing from here.

Thanks for the feedback about your solution. I'm sure somebody will make good use of it.