How do you unlock ricky steamboat in Smackdown vs Raw 2011?

You have to complete all challenge matches in Chris Jericho's Road To WrestleMania, and then, at WrestleMania before you face Triple H, go to the green room to find Ricky Steamboat.

All of the challenge matches for Jericho's RTWM:

Week 1 - Singles Match against The Miz

Week 5 - Singles Match against Santino (talk to Santino at the Royal Rumble to set this up)

Week 7 - Parking Lot against Cena

Week 8 - Diva Match against Maryse vs Beth

Week 11 - Singles Match against Santino vs Big Show (talk to Santino in the hall to setup your interference)

WrestleMania - Singles Match - FindSteamboat in the Green Room