You cannot override the settings as windows 2K sets them to 256 when a client logs on,
If you only need more than 256 for installation of the product then install VNC (Like Terminal Server) on the server, connect with VNC Viewer and install application then uninstall VNC from the server and carry on using Terminal Server.
VNC is free and can be downloaded from
http://www.uk.research.att.com/vnc/