Scrolling Down + Ctrl moves elements

I'm practicing PSD to HTML (this being my first time doing it). The page renders well in both Chrome and Firefox but when I scroll down pressing control (to shrink the page) some of my elements move around (which I'm pretty sure isn't suppose to happen). I though it had something to do with a missing or maybe some bad width somewhere but I can't figure out what's going on.

I've put my work so far there: [link removed]

any help much appreciated!

Seems to work fine on MAC and Fireworks zooming in and out - can't help anymore than that.