CSS layout - margin problems

[Susie56]

I am trying to create a gallery for a friend of mine and can't understand why my images will not go across the main column, it seems as if it is a 3 column layout instead of a two column website. The domain is here: http://www.smiths-houseclear.co.uk/portfolio.html and the css is here:
http://www.smiths-houseclear.co.uk/house-clear.css I meant to say that I require 4 images on each line.

Plus the images are overlapping, suspect that's the same problem though. I have successfully created these sort of galleries before, but seem to have lost the plot with this one. Any help would be greatly appreciated.

Susie

[Deadweight]

try this:

#contentcolumn{
margin: 0 180px;
width: 80%;

}

#leftcolumn{
float: left;
width: 20%; /*Width of left column in pixel*/
margin-left: -872px; /*Set margin to that of -(MainContainerWidth)*/
background-color: #ffffff;
border-top: 2px solid #53ACE0;
border-right: 2px solid #53ACE0;
border-bottom: 2px solid #53ACE0;
}

[Susie56]

Thank you so much, it is fine now, better idea working with percentages.

Cheers Susie

[Deadweight]

Yep no problem