Since team fortress 2 and source SDK have been freely available, you don't have to have CSS in order to setup CSPromod.
- steam -> library -> tools
download and install Source SDK Base 2006 & 2007
- run Source SDK Base 2007 at least once
- if you have CSS, skip this step; else, download the following file and put it in the following directory
- download both of the following CSP patches and extract them to the following directory
- restart steam