Use this shader and the 2 materials I'm posting for you, it should give a nice dirty looking glass effect:
textures/amph_materials/glass_dirt
{
qer_editorimage textures/amph_materials/glass_dirt.tga
surfaceparm trans
surfaceparm lightfilter
cull disable
{
map textures/amph_materials/glassfx.tga
blendfunc add
tcMod scale 0.5 0.5
tcGen environment
}
{
map textures/amph_materials/glass_dirt.tga
blendfunc blend
alphaGen wave sin 0.3 0 0 0
}
{
map $lightmap
blendfunc filter
}
}
Obviously change the paths to whereever you want the textures.
Save these as:
glass_dirt.jpg
glassfx.jpg
I'll get them in the texture pack I'm doing and get them all GPL'd for you.