Both columns same height as deepest column?

Answer 1

Adapted from here:

Create a container around the two fixed columns, and have css something like this:

#container {
    float:left;
    width:[sum of the two columns width];
}
#fixedwidthwide {
    float:left;
    width:[whatever];
}
#fixednarrow {
    float:left;
    width:[whatever];
}

Note that this is only necessary if the columns need to be of equal height for some reason. If not, you can just follow philfreo's suggestion and use faux columns.