Successfully complete the indicated task in SOCOM: U.S. Navy SEALs - Combined Assault for the PlayStation 2, then link to that game to unlock the corresponding character in Multiplayer mode:
Jester: Successfully complete Campaign mode in SOCOM: U.S. Navy SEALs - Combined Assault with an "Admiral" rank.
Killjoy: Successfully complete Campaign mode in SOCOM: U.S. Navy SEALs - Combined Assault with a "Commander" or higher rank.
Simple: Successfully complete Campaign mode in SOCOM: U.S. Navy SEALs - Combined Assault with an "Ensign" or higher rank.
Bonus Multiplayer items
Earn the indicated number of Command Equity points to unlock the corresponding items in Multiplayer mode:
To get more money, play your campaign over again. To do this, go to your "Profile Data" screen and look up "Reset Campaign". If you do this it will not take away from the other things obtained with the last campaign. All you need to do is find new things that you did not find originally. Also, all your campaigns will be in the 300 to 900 in your money. Keep going back to this every time.
Fly into next room in Private Estate level
In the Private Estate level, go up to the second floor and find the stereo. It will have the "Use Stereo" action. If you walk up to it, you will notice that you can stand on it. Walk up to it and as you are going up, activate it. You should fly a few feet away. If done perfectly, you will go into the next room.