If you want a retail copy you must buy the orange box. For a while it came bundled with HD2600XT's in the black box. You can buy EP 2 through steam, but it's $20 just for it without TF2 or Portal. I like Portal alot, and am now hooked on TF2. Ep 2 was very good too. The orange box is worth the money IMO.
Isn't there anyone you could give the other two games to?