xterm keymappings

Hi, I need to map or enable certain keys within a single instace of (preferably) an xterm. I telnet into a machine on our local network that runs an app on a SCO background. If I select vt220 keyboard for xterm I can get keys F1-4 OK but all the others are non-functional. The mappins I need eo emulate are in this format: F9 = ESC OX F10 = ESC OY etc etc. If I type the maps I get the functionality I need but typing for instance: ESC [@ is not easy. Please would someone be so kind as to suggest how I can launch an xterm ( ? via a separate launch script ) that will enable me to remap as needed? Many thanks Francesco