DX10 is broken since Book 14, I was getting mad, thinking it was all because of the ATI drivers, but no. All other DX10 games I have tried (Devil May Cry 4, Lost Planet, Hellgate London) work with no problems, only LOTRO crashes. But there is an official crash report thread
for Book 14 where people with both ATI and nVidia cards are getting crashes on DX10. I have played for an hour in DX10 with no problems, but doing nothing, just walking or riding from zone to zone. If you enter a fellowship and start fighting, it will crash after very few minutes.
It has been included in the list of known
issues of Book 14:
If you have DirectX 10 enabled you may experience crashes. Turning off DirectX 10 will solve this issue