- icefirei
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- Noble Heroic Member
If you're talking about Halo 3, it doesn't have anti-aliasing (as far as I know) so is susceptible to the jaggies. Other than that, a bad cable isn't likely to give you jaggies. Check that your tv is set correctly, and your xbox 360 is also set to 1080i. If you still see lots of jagged diagonals in games other than Halo, then it might be something else.
On a side note, does your tv support 1080i via component cables? I've found that often 1080i looks better through component than it does through HDMI, so you might want to try it and see what you think, if you haven't already. You don't really need to be using HDMI at that resolution (unless your tv requires HDMI for 1080i)...