I have been using the EXPORTTOAUTOCAD2000 command in ADT 2004 quite a lot in the past week and have made an "interesting" discovery. If the default plot style type, as set on the Plotting tab of the Options dialog, is not the same as the plot style type of the drawing you are exporting back to AutoCAD 2000, the plot style type of the exported drawing will be the type specified as your default in Options, NOT the type of the source drawing file. I was not expecting this behavior - I only noticed it while checking something else in an exported file.
In the Page Setup dialog, the plot style file specified in the source file remains, but is noted as "missing". At least the default plot style file is not substituted, which would leave anyone opening the exported file completely unaware that a change had been made.
I now have a profile set up that is similar to the STB default one I generally use, but which has CTB as the default plot style type, for occasions where I need to export CTB files.
I am happy to report that ADT 2005 does not change the plot style type of a file being exported to AutoCAD 2000, even if the default plot style type is different from the plot style type of the drawing being exported. This is yet another reason to upgrade, or to install ADT2005 from that disk in the box on the shelf.