You can convert Quake textures to HL using Wally. (can't remember where to get it...). It can load quake/hl textures and save them as quake/hl textures. I've done it before infact and I might still have the textures I made from quake for HL if you want it although some textures wouldn't work due to bad filenames for HL textures.
edit: infact, I found them, I'll upload them to the filebase!
No see what I need to do is dump a texture lump from a Quake map, add the palette, and modify the other lumps' positions. Or be lazy and put the textures at the end of the file.
Hmm, so what are you trying to do? Convert Quake maps to HL map basically? I done the same thing by using the textures above and winbspc to decompile quake maps and compile them as HL maps....
I'm kinda lost though, I'm sure I'm still not getting to the point