Uncheck the HDR ( last bar at the graphic settings sett it to off ) and you should be able to change AA again.
Thought if you want REAL AA, you should use your graphic card settings instead. If your using Nvidia I recommend a program called nHancer http://www.nhancer.com/
I'll second Ple's nHancer recommendation. The AA in L2 is really slow (or at least was when they first came out with it); my vid card can do 8x AA/16x AF and have a higher framerate than 4x AA in L2.
If you use your graphic card itself to set the AA, like nHancer does, be sure to disable both AA and HDR in L2.
BTW my preferred L2 settings in nHancer:
Antialiasing - 8xS Combined
Anisotropic Filtering - 16x
Performance - High Quality
Negative LOD Bias - Clamp (I am not sure this is needed though)
Your mileage may vary. It wasn't unplayably slow, just not as good as I could achieve using my vid card's programs (nHancer is basically a more advanced/less buggy GUI than the nVidia default, but it uses nVidia's graphics profiles).
Plus I really appreciate the anisotropic filtering in L2. The 'pixel swimming', especially on the ground textures, was worse for me than the jaggies.
For Ledaa:
Anti-aliasing helps to smooth the jagged edges of models. If you look at a straight diagonal line on some model in L2, you'll see there's kind of a "stairstep" effect; AA helps to make the line look straighter. Aliasing, in this case, is where the straight line doesn't look straight when rendered because you can't, for example, make part of a single pixel black and part white. Antialiasing would effectively make the pixel some shade of gray depending on how much black and how much white it should be.
There are different methods to do antialiasing but a common one is to render the whole image at a higher resolution, so if you're playing 1024x768, it may internally render it as 2048x1536 and then blend adjacent pixels together to create a 1024x768 image. There are even more clever methods that only do that high-res rendering just at the boundary of models, where aliasing is most pronounced.
Anisotropic filtering helps to remove another kind of aliasing, caused by needing to stretch or shrink a texture based on camera angle, distance, etc.
Could you explain more about where to turn off HDR at? I can't seem to find it in the options menu at all. (Maybe a screenshot?) :) I also used to be able to turn on AA and reflections ingame. Now neither one of them work. I updated my graphics card driver (GeForce Ti4600) about the same time I updated LineageII so I'm not sure which stopped it from working. I've tried a few different drivers since, and no change. I haven't noticed any difference in quality of the graphics, but I did like the reflections on the water. :D Thanks
Your card shouldn't even support HDR so you won't be able to have it enabled, probably under the same reason why you can't enable reflection nor AA because both use functions only in DX9 cards.
The wierd thing is I know I've been able to enable AA and reflections before. I'm pretty sure it has something to do with the driver though. But anyways, it's all good. :)