Be a dragon slayer
Enter on cheat screen of the game one of these:
4draslay - dragon blade
g2hoppy - super jump
nbyhigh - be tall
meskk6 - unlock everything
pfhr557 - sword
You'll have to complete the desired achievement to receive the allotted gamerscore:
Awakening (50) - Completed Dragon Age: Origins - Awakening.
Pride Before The Fall (30) - Defeated the baroness.
Blind Vengeance (30) - Escaped the silverite mines.
Commander of the Grey (30) - Reached level 30.
Savior of Kal'Hirol (30) - Destroyed the broodmothers in Kal'Hirol.
The Enduring Vigil (30) - Acquired all upgrades for Vigil's Keep.
Amaranthine's Last Hope (25) - Saved the city of Amaranthine.
Keeper of the Vigil (25) - Saved Vigil's Keep.