Here's how it worked: Houshmandzadeh signed with the Baltimore Ravens, improving their depth at the position, and the Ravens then traded 2005 first-round choice Mark Clayton to the Rams, according to ESPN's Chris Mortensen. Baltimore presumably deemed Clayton more expendable after picking up Houshmandzadeh, a more consistent performer.
Clayton's talent as a receiver is obvious, but his production has been inconsistent. A detailed Scouts Inc. report on Clayton says he's strongest on timing routes, and the Rams are big on timing routes. Clayton will not necessarily flourish in St. Louis -- he has much to prove -- but he'll give Bradford another potential weapon following Donnie Avery's season-ending knee injury. Sounds like the Rams are also getting a well-liked player.
The Rams have spent the past couple offseasons piecing together their receiving unit. They acquired Laurent Robinson from the Atlanta Falcons before last season. They signed Danny Amendola off the Philadelphia Eagles' practice squad in September 2009, then acquired Brandon Gibson from the Eagles in the Will Witherspoon trade a month later.
The Rams haven't confirmed the deal, presumably because they'll need to make a roster move. The Rams already have six receivers. Keenan Burton and rookie Dominique Curry earned the last couple roster spots at the position. Curry has tremendous size and he was a force on special teams during the exhibition season. I'll update this item with the corresponding roster move once the move is made.
Update: The Ravens have confirmed the trade, revealing they will receive an "undisclosed" draft choice as compensation. ESPN's Adam Schefter says the Rams sent a sixth-round choice to the Ravens for Clayton and a seventh-round choice.