Things like this make me giggle.
Most of that came from the make-your-K6-2-into-a-C64 post I wrote a couple of weeks ago, with one small addition: The greeting message that goes in your .bashrc file. (I did this in Arch, although it should work in Ubuntu too.)
The message only appears on the first spawning of a terminal (or when you log in to a tty1 screen). If you wanted, you could code it to check the status of the terminal and see if that message should be displayed. Regardless …
PS1='\nREADY. \n'
echo
echo " **** COMMODORE 64 BASIC V2 ****"
echo
echo " 64K RAM SYSTEM 38911 BASIC BYTES FREE"
Note the leading spaces on two of those lines; you need those to get the greeting centered across all 40 columns. And there are two spaces between SYSTEM and 38911.
After that, just grab the Adore64 font from Freakyfonts.de and unzip it into your ~/.fonts folder. Add this to your ~/.Xdefaults file, to tell urxvt to mimic the dimensions and colors of the old C64 screen.
urxvt.font: xft:Adore64:autohint=false:antialias=false:size=6
urxvt.background: #3a319c
urxvt.foreground: #7b71d6
urxvt.scrollBar: false
urxvt.cursorBlink: true
urxvt.geometry: 40x25
After that, you could set up some aliases between the old C64 commands and bash commands. Set load"$",8:list to ls, if you want. Or sys64738 to sudo reboot. That would be pretty funny.
But I’ll leave those things to you. I mean, there are limits, people. 
I did something similar, only I never made it look like the C64 Terminal. But I wrote a simple tutorial on how to add a message to the beginning of your terminal too, awhile back:
http://php.8ez.com/drsmall/blog/?p=164