Banner width in resolutions

[RedTrinity]

Hi guys,

Well at the moment I have a banner problem I am hoping to find some help with!

We have an 900x130 header banner for our forum, but the problem is that the forum alignment with the banner changes in different resolutions

With low resolutions, the forum/banner alignment appears fine. But in higher ones (like mine), the forum is too wide and the banner is about 10cm off on either side. Then of course if I increase the banner width to match the forum for higher resolutions, it causes a horizontal scrollbar issue with lower ones as the banner becomes far too wide.

Is there a way to get around this problem? Our forum needs some kind of header, but I dont know what I can do to get around this problem. How have other people dealt with it?

Here is our forum: http://www.theparentingsanctuary.com.au/forums

Thanks in advance for suggestions!