risking you might find me odd but is there a way to use the "desktop" used for the installation later with the real thing? it reminds me of ultrix, just nicer. that ruby bg color and the golden wristwatch icon sort of got me
If it is twm, it should be pretty basic in terms of what it would require to build from source. You should be able to grab it from a plain X11R[4-6] distribution - check a local site (US mirror, EU mirror)...
after quite some searching i found it and modified it a bit. stop xlogin and run this. you also need to copy 2 files from the inst cd: Xdefaults and mwmrc. both located in /isl. easiest way is to create a local /isl and put the files in there. otherwise edit the script accordingly.