I have never been able to go down in the cellar at the Warriors Guild or at the Imps Fortress.
I found that if I just enter the door at the Warriors Guild and hold the pointer over the steps and double-click, I find myself in the cellar. Using that, I found if I approached the cellar steps at the Imps Fortress just to the right and outside the room, I could do the same thing. See the attached image for an approximate location of my character.
I had the res set to 1024 x 768 at the Warriors Guild but had to set the res to 1280 x 1024 at the Imp Fortress for that to work as I could not see the steps at the first res, probably both work at 1280 x 1024. When you are at the right spot, the steps glow white instead of red. Just double-click and you're in!
Worked for me so I thought I would share, I may be the only one that couldn't get to the cellars !. . . =^ )
It might be interesting to find out if this works for everyone or just a few. How about posting your results yes / no , OS and video card mfg if you try this?
Edit: Just clicking on the ladder puts you back up stairs as it should.
Edit 2: Did the Warriors Guild quest first since that sends you to the Imp Fortress.
Edit3: Had two Dwarf teleport scrolls in my inventory, removed one and was than able to activate the Imp teleporter

hm! that's awesome! I dont know if i can support that resolution, but ill try. i definitely need to build a new computer (and buy an xbox... and an hdtv.. sigh*)

Your workaround has just worked fine. Now I'm a member of the warriors guild
Thank you for sharing this.

Great, happy to share any progress! It was frustrating not being able to do those quest.

Thanks to you I was able to do the Warriors Guild quests and activate the imp teleporter. Thanks!

I'm so glad to hear it works for you and others, I was concerned that it might only work on my system. Since then I have overcome Josephina (I cheated) and now find myself in the land of the dead . . .=^ )

Stuff ......you win the Divine Divinity Cookie Award!!!
I was all set to stat over again, had reinstalled etc etc
Thanks a ton.
Any ideas for the cave in the dwarven halls? =(

You're welcome, always glad to hear it works for others. I had no problems with the mines (bugs, that is), don't even remember a single crash there. Might look over this link for hints http://www.gamebanshee.com/divinedivinity/locations/dwarvenmines.php and there are some other links in a walk-through post here in the DD forum.
I managed to finish the game over the weekend, waiting on the patch to give it another try . . . =^ ) . . . good luck with your game, I really enjoyed it in spite of the problems.
Edit: I DID go slow . . .one room at a time in the mines!

Sweet,
I just recently got to this part of the games and was getting really frustrated with not being able to get into the Warriors Guild Basement and the Imp's fortress
Got to go try out this out.
edit
Confirmed - I was able to access the crypt under the warriors guild
Thanks for posting your find Stuff

Thanks a lot, a have the same problem. Than i just step into door and stair become white and i cold go down.