You can now play Battlegrounds 2 completely for free! The kind people at Valve have made the Source SDK Base 2007 available to anyone with a Steam account.
All you need to do is:
1. Install steam (http://store.steampowered.com/about/) and create an account.
2. Go to the Library page in steam.
3. On the drop down menu, which should say “ALL GAMES”, select “TOOLS”.
4. Scroll down to “Source SDK Base 2007″ and double click it.
5. Install the “Source SDK Base 2007″.
6. Download the Battlegrounds 2 Installer. (http://www.bgmod.com/downloads/bg2w.html)
7. Run that installer.
8. Restart steam and Battlegrounds 2 will be in your installed games list.