To unlock this achievement you must either play in Dynasty Mode or Campus Legend Mode (remember to only select a SINGLE team and not multiples). Then your team must be invited to the BCS championship and you must win it. Please also note you must PLAY or SUPER SIM in the game for the achievement to unlock (see below for more information).
Now the BCS is the Championship game after playing in the Conference game. So it's very hard (sometimes) to get invited to a BCS game. So to increase your odds be an undefeated team and win the conference game then you might be invited.
There are multiple ways people suggest in how to do this but this is how I did it... I played in Dynasty Mode and selected Florida University (the Gators) as my one and only team. I then proceeded to sim though the season one game at a time. If the score was close or I lost the game I would re-load but if I won I would save and then continue to sim the next week. I continued this until I was invited to the SEC (Conference Game).
Now you can sim this Conference game until you win but what I did was played the game and won 49 to 7 (not sure if a high score matters or not) but sure enough after finishing the game I was invited to the BCS. I highly recommend SAVING once you get invited. Just in case you play and lose you can go back :)
The hard part is now over. Remember you must PLAY this game so don't sim over it, so select "play this game". Super SIM is awesome, when you can call a play (does not matter if it is offense or defense) press start and then select Super SIM. You can see the score, quarter, and time left (lower right hand side of the screen). Just keep pressing A button until the game is over (if your team is winning) or if you start to get behind just press the B button to play again and go score some TDs!
Do this until you win the game and the achievement is yours!
If you do play and win a game it is suggested that you delete your cache and then try to replay the game. Thanks to Curtieson for this!