I'm developing a wordpress theme at
http://ap-gfx.com

and now I have a problem. The sidebar should not have a gap on its right side.
does anyone know how to fix this?

I had a look at the source and the CSS and i'm sorry to say I couldn't find the problem. Then again, I probably couldn't force that horz. scrollbar like that if I tried.

I just looked at the CSS your wrapper is set to 100% is that the problem?

Give your wrapper a fixed width and set your right column to "float: right;" or left... give it a width too, and set your positioning relative.

For example:

#wrapper {
width: 800px;
}

#left {
width: 200px;
float: left; position: relative;
}

#right {
width: 600px;
float: right; position: relative;
}

When you have a div coming underneath it, you give it:
#bottom {
width: 800px;
clear: both;
}

Should work.