Counter-Strike, IIRC, you can buy boxed with or without HalfLife. The main reasons to get it boxed are the documentation and convenience (having it on a CD, without needing to download). But you can get it Online, legal and free.
Ways to make the game harder against AIs:
Small galaxy
NO Neutral Empires
Turn off surrender
Use AI-friendly maps (low storm, black hole, asteroid system percentages; in other words, don't use Ancient quadrant)
TDM AIs
P&N mod as either a Pirate or Nomad
Self-imposed restrictions (eg. capture all planets, no planetary bombardment; don't use intelligence; don't use any racial points)
Ways to make the game harder:
Play humans
