my bad, i had it wrong. here is what espn reported:
"Jackson agreed to a two-tiered deal with the Rams. It's either a three-year extension worth $29.3 million with $21 million guaranteed, or a five-year, $49.3 million contract that includes huge escalators in Years 4 and 5, a source told ESPN.com's John Clayton.
The way the contract works is that it is structurally a five-year deal lasting until 2013. The final two years can be voided based on Jackson's performance, but his performance can also trigger the escalators to take the five-year deal to $49.3 million.
Though a breakdown of the triggers of the deal isn't fully known, a source told ESPN.com that Jackson has to perform similarly the next three seasons to the numbers he put up from 2005 through 2007 to fulfill the escalators."
http://sports.espn.go.com/nfl/trainingcamp08/news/story?id=3546615