How do I copy a toolbar between machines

The toolbars are held in the Workspace file, these are *.tb files. If you have a custom workspace file, you can move that onto the other machine. If you have customized the Default workspace, then you can copy that as well of course but it is best to SaveAs to a new name so that reinstalling Rhino and the default.tb workspace will not nuke your changes. Default location for the .tb files is:

C:\Documents and Settings\All Users\Application Data\McNeel\Rhinoceros\3.0\default.tb

If it is only some toolbars you want to import into an existing workspace, you can use Tools>Toolbar layout> Toolbar menu (in the dialog)>Import. Navigate to the workspace file (currently .tb but also could be the older .ws and .ws3 files) and choose the toolbars to import. More on all this in the Help files. - Pascal
Rhino Newsgroup