1280X960 or 1280X1024 resolution?

Trilinear filtering is what "came before" Anti-aliasing (anti-dent filter) so the order of antialiasing is bilinear, trilinear, AAx2, AAx4, AAx6, AAx8.

It depends on the monitor you have. Choose the mode you see better. If you feel the image is streched in some direction, try the next resolution setting.

Your monitor has a 4:3 ratio (it's a little more wide than that it is high). 1280x960 translates to the same ratio so if you pick this resolution, the pixels on your screen will be square (provided your monitor settings are ok). 1280x1024 is a 1.25 ratio. Is all of this relevant? Not really. Most, if not all software can handle non square pixels so you can just adjust your monitor settings to get the right display of the graphics on the screen (non stretched so to speak). Why is 1280x1024 better? Because you get more pixels on the screen = nicer image. If you get stretched images (or the other way around) fiddle with your monitor controls until it looks ok again. The amount of pixels on your screen has no direct relation with how they are displayed, your monitor has certain internal presets that it applies when receiving a signal but you can modify those to get the correctly sized image on your screen.

Personally with that card I think you should go to 1600x1200 if your monitor can handle it at 85Hz or up. With regard to filtering. Go as high as your card can handle (see snale's reply) while retaining a good framerate.