The majority of MMOs (including LOTRO) don't have OS X clients. Sad, but true. If you really want to play, you have to pony up for a copy of Windows and install it with Bootcamp. If you're running Vista or 7, you'll be able to be able to use DX10 graphics. Very pretty.
I play LOTRO on both my MBP and MP in Windows 7 x64.
On my MBP (2.6GHz with 8600M GT 512MB), it runs acceptably with most of the eye candy turned on at native resolution (1440x900). But I usually keep things like shadows and high-res textures turned off because it's a huge performance hit in crowded areas. But don't play on your lap. It gets quite hot!
On my MP (2.8GHz Octad with 8800 GT 512MB), I run the game with all eye candy turned on except for anti-aliasing at 1920x1200. I rarely see dips below 40 fps (about 80 fps on average).