Where are the half life, etc. dialog files kept ?

I want to extract some (with gcfscape, I guess) to use in machinima. Where in the file structure are they located exactly?
Thanks!

Your Drive (C:// or D:// or whatever) / Program Files / Steam / SteamApps / (your steam name)

Ah, found them in source sounds gcf. I had peeked in there, but missed them since they were listed by location, not character. My bad.