I think I still have DHTML Fun levels 10-20 or so sitting around somewhere. If you're interested I'll see if I can find them.
As to the exit disappearing, it's due to the way the images are layerd in dhtml lemmings. The problem is that the exit has to be below the terrain to be hidden, but the bash/mine/dig masks have to be above the terrain. This means that the masks will also be above the exit. I'm afraid there probably isn't any way to do this correctly in javascript.
Also, if anyone still needs the graphics, I have the complete original version including graphics and sound.
Cheers,
Zen