Definitely a card problem. The "intelligent" filtering shemes were implemented on GeForce 2 or even 3 ... the ones before were very incapable, but enough to what games that day needed: At least some filtering to prevent the massive problems you get without it.
Around GF2, the new perspective filtering shemes came in (first screenshots showing them were CounterStrike pics if I remember correctly) that prevent the problem you describe: bad results on k*90 + 45 angles.
Around GF2, the new perspective filtering shemes came in (first screenshots showing them were CounterStrike pics if I remember correctly) that prevent the problem you describe: bad results on k*90 + 45 angles.