Dear Steven;
I am assuming you are using a paper roll fed plotter of some type. If so in the plot dialog for AutoCad 2000, select plot device tab, select your printer, properties, custom properties. Hopefully a dialog will emerge which allows you to configure a custom sheet size. Trouble is, the dialog varies with the plotter you are using.
If you were able to plot oversize with version 14 though you must have had this size already set up within the plotter. Using Version 2000 wont change the printers configuration. The drawing size should still be available on the dropdown list of paper sizes.
Regards Adrian