Thanks for the pic Obese87. I don't really know what would be causing that, but it might have something to do with the way a .png is rendered on the browser.
Very odd.
EDIT: Increased the width of the banner to 3000px, so hopefully it should get rid of that line now, plus it should fill most monitors.
Quote: "I must say your skin is very clean and easy on the eye.I don't see a problem on Chrome."
Thanks! I spent a lot of time trying to get the design as clean and open as I possibly could, after many attempts, this is the one I came up with.
Quote: "
I personally HATE Internet Explorer , especially IE6 "
Surprisingly I've had no major problems with IE7, and no problems at all with IE8. IE6 however, as you can expect. Complete shambles. Might just make a separate design for IE6.
Quote: "Tip - Stay away from background images that are not seamless lol"
I learnt that lesson a long time ago.

Although CSS 3.0 with multiple background support should change this.
Cheers for the comments.