Easy "Star Performer" achievement - Play the San Francisco level in Co-op mode. With another skilled player, you should be able to find all the cards and items quickly enough to earn an "Elite Agent" rank and get the "Star Performer" achievement.

Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Finder's Keepers (20 points): Find all 8 Items in a City Location in the Single Player or Co-Op Mission.
Quick on the Draw (10 points): Find 3 items within 5 seconds.
Bonus Plan (10 points): Find all 9 Bonus Items in one Mission.
Not Impossible (10 points): Complete one Mission.
The First Hint's Free... (10 points): Complete one Mission without using any Hints.
Just Said "No" (25 points): Complete every Mission without using any Hints.
Wham, Bam... (25 points): Complete a City Location in less than 30 seconds.
Star Performer (25 points): Earn Elite Agent Rank in any Mission.
You Always Remember Your First (10 points): Complete Mission 3 and capture Mister Smith.
Back for Seconds (15 points): Complete Mission 6 and capture The Hammer.
Third Time's the Charm (15 points): Complete Mission 9 and capture The Artiste.
Fourth Down (25 points): Complete Mission 11 and capture Dr. Chaos.