Welcome to the forums! Obsidian is based off of the Source SDK Base, as all mods should be now. Valve added it so when they update the engine on one of their games, it won't screw over mods until they release new code. So just let it download, it's normal. Hope you have fun with the mod .
ohh aawww magicly mabey you just never look at YOUR CASH FOR A LONG TIME!
I got owned once...Its not pretty.Now a message from our news zombie Joe Carl Joe!(The news zombie)Obsidian Conflict needs a nice automatic shotgun! Jackhammer perhaps?*Farts*