Right, i'll try my best
Triple buffering basically allows for more filtered textures and objects which look better, without much performance hit. The normal amount is 2 times.
Force 24-bit-z-buffer forces the card to use 24bit instead of the usual 16bit for managing 3D games where it goes into the screen (for instance, first person shooters) an basically allows for better quality if your card supports it of distances...i think
Geometry instancing is on new cards. Basically it is supported in DirectX 9 and allows for cards to render objects that will be repeated over and over in no time at all without any extra work.
For instance a forest could use geometry instancing to make loads of trees. The card would only have to render once, and it'd just copy it over and over to the specified amount by the programmer.
Alternate pixcel centre, i've never found a use for. Basically if you change that, the pixels and some polygons seems out of place....
Anti-alising basically smooths corners of objects and thnigs. Think of pixels on the monitor as blocks, if you drew a diagnal line, they'd look like steps and not a smooth transitioned line.
Basically anti-alising smooths colours together to try to hide this stepping by placing colours that match the colour on screen so that they seem to hide the effect. This takes alot of GPU power though as it has to smooth every pixel. 2x,4x, etc would just increase the amount of smoothing in play.
Antistropic filtering doesn't seem to use that much GPU cycle time, and basically tries to smooth out textures, and filter them in the same way anti-alising does for the look of the objects except It makes textures sharper and more defined.
If you view a road for instance from a far, it increases the amount of filtering lines that make the road look more defined as it gets closer to you. If you look carefully, you can see them in games, and usually consists of about 4 filters on the screen (4 lines, and textures seem to get better as it passes a filter) (4x) which dramtically increases the look of the game
If you have the Catylist control centre, you can view these changes with a 3D car that moves in a 3D world as you change settings in real time.
I hope this helps