Photoshop/ Illustrator delinquency

[SRD Art]

Getting a drawing ready to post for the art show tomorrow. I did most of the work in Illustrator and then brought it into Photoshop for some highlights and stuff and as I save it to a jpeg, I found that a large 11" wide file looks pretty good on the screen. When I shrink it to 8" wide at the same dpi the straight lines that make up the stripe that spans the side of the car and are angled down get choppy, while the rest of the artwork looks great. If I zoom in the lines look better, and if I print it small or large they look nice crisp lines. This has happened to me before, it's just straight lines that are at an angle that get choppy when I save it to a jpeg, the rest of the image looks fine. Any ideas why this happens?

PS I use photoshop 6 and Illust CS2.