First I import the footage, which is H.264 .mov (mpeg-4 .mov and mpeg II .mov yield the same results), then I drag it onto the 'new comp' button to make a new comp with it, and the footage appears as if the diagonal lines are not anti-aliased.
Example:

Yet the footage appears perfectly fine in other media players, and double clicking the file in the project panel shows it perfectly:

I've tried changing view/display/render options to highest quality or 'full' resolution, and nothing changes the footage. I've checked the 'interpret footage' window and 'separate fields' is set to off. Rendering the clip using the default 'best quality' and 'lossless' gives the same quality as I see in After Effects.
Converting it to 'DV' footage with ffmpegX fixes the weirdness, but is really big, somewhat squashed, and on 2x speed O.o
It's possible I'm missing a setting somewhere, but I won't know where else to look. Does anyone have an idea on how to fix this?
I have a possible theory on this, though:
The source video is identified to be 720x480 (16:9 video, no letterboxing), yet converting it with 'size and aspect-ratio as input' gives a video that is 853x480, yet this videoframe is the same size as the source. Could the problem lie here somewhere in this discrepancy?