Ahh... in short: You can't... well not easily.
A search through this bulletin board will probably reveal people who've tried. I'm not sure how much success they had.
Midnight Commander (mc) is installed if this helps.
"Why?" You ask.
A full blown GUI was deemed innapropriate for a 'turnkey internet appliance' thingy.
Hopefully the maintence thats required on the command line with SME is small and the web interface should suffice for the bulk of your maintence needs.
eg. I, like a lot of SME admins, don't actually have a screen, keyboard or mouse plugged into the server box at all. It just sits in the corner, doing it's thing.