You may want to try running in software mode instead of OpenGL (if you're not already doing so). I doubt that using OpenGL would only affect LoD and not D2 by itself. But it's worth trying since it's such an easy change.
It's possible the problem may be related to your software install. I can't rememeber LoD ever causing a freeze or crash on any of my Macs. There's maybe a small pause while the game spins up your play disc (CD) if you haven't copied over enough of the files to your hard drive. But an all out crash or lockup has never happened to me with D2/LoD. And I bought the game early on - playing it on Macs ranging from OS9/G3 iMac all the way to my current dual G5 Tower running 10.4.8. Maybe another MacIntel owner could post their experience with D2/LoD.
After all this time, D2/LoD is still one of the my personal favorites. It was money well spent! If Blizzard ever releases another expansion pack or modern update to the game (IE more than 800x600 res) I'd buy it sight unseen!! Thanks Blizzard!