Using the same ctb file and dwg file, the line weights do not match between AutoCad and MicroStation XM.
When plotting from AutoCad, there is an option to "Scale lineweights". In AutoCad 2004, this is on the Plot Settings tab. If this is selected, a scale is applied to the line weights set in the ctb. If you turn this off, the plot from AutoCad will match the plot from MicroStation using the same ctb and dwg file.Another solution would be to create a MicroStation pen table that assigns line weights based on the scale being used in AutoCAD.