I had an idea of a hallucinogenic map thingy once. Maybe you could have a large box you enter where the walls are .bik's that have this http://www.youtube.com/watch?v=l-_NneB5fmY&feature=related The youtube video has a link in the description to the program where you can alter the variables to change the speed and colors and size . It makes your eyes go funny and everything you look at seems wobbly.
Anyway, making the road textures slightly transparent would be pretty easy. If you wanted to be fancy you could even have the texture as a .bik so it can change colors and things.
I think making the hud invisible is possible if you make a "menu" folder in your map and replace all the hud .dds's like health bar and player icon with transparent .dds's.