Use UltraTreeNodeColumn.LayoutInfo.PreferredLabelSize to adjust the column header size; cell widths will pick up the width under OutlookExpress.
UltraTreeNodeColumn exposes a 'Format' property which you can use to control how cell values are depicted.

Example:
int columnWidth = 200;
TreeColumnsCollection columns = this.ultraTree1.Nodes[0].DisplayColumnSetResolved.Columns;
foreach( UltraTreeNodeColumn column in columns )
{
    //  Set the column width
    column.LayoutInfo.PreferredLabelSize = new Size(columnWidth, 0);

    //  TODO: Localize the currency format
    column.Format = "$#,###.00";
}