get hlmv (half life model viewer), open up the pak0.pak file (or w/e it is for hl2, if there's no pak0.pak look around, there's somthing like that) in your valve directory. gfx/env - that's what folder in hlmv in pak0.pak hl1 holds all the backgrounds. have a looksee, i'll check it out tomorrow about what the file is called