Theres your problem. You have a pre-live dash. You don't have a Live tab on your originial M$ dash, and you also don't have a "Fonts" folder on your C drive. I'd be willing to bet if you upgrade the dash to the 4920, then run the installer, all your xbox dreams will come true lol.
My suggestion is the Slayers Auto Installer (unpack that iso with quix, xiso or
something along those lines), then ftp into your box, delete everything on C: and ftp the files from the RETAIL/ALL/C directory to your box and you've got yourself the 4920 dash.
An alternative is to use a Live enabled game (return to castle wolfenstein has the 4920 dash) and select Xbox Live. It'll upgrade the dash for you without requiring you to connect to anything. Give those options a shot and let us know how you make out. Feel free to PM me if you really get stuck.