1) BSP file, like de_inderno.bsp
2) Textract --> http://www.superjer.com/files/textract.zip
3) Put them in the same folder
4) Open a command window there
5) Type: textract de_inferno.bsp de_inferno.wad
6) And press enter
That's what you do to textract from CS1.6 maps. I don't know if it works for source, probably won't.