NCAA Football 07

Ok, so the first two solutions just didn't do it for me. Hopefully I can help some of you that don't quite know what to do.

First, begin a new dynasty.
Choose the top 12 ranked teams.
Sim the entire season until you get to the offseason.
In the offseason you are going to want to sim "Players Leaving" and "Transfer Requests."
After that, click on "Recruiting" (if you aren't brought to that screen automatically).
When you are in there, press Start and sim through all the weeks.
Once that has completed, a menu will pop up and you will want to click on "Top Classes."
There, you should see the teams in order of rank; the highest rank will be at the top of the list.
Your teams will appear in yellow.
Chances are one of your 12 teams in yellow is ranked #1. (If not I suggest you make a new dynasty and retry until one of your teams is.)
If so, press RB until you've made that team your active team.
Next, press B to go back and return to the Offseason.
Click on "Recruiting" again and this time select "Finalize Recruiting."
Once that's finished your achievement should pop! :)

Leave comments/questions if needed.

I chose the higher ranked teams (12 of them) and started into a Dynasty with them. This unlocked on the first season for me. Alot of achievements in this game are unlockable through simming the Dynasty - including the 60 years one..

Start a new Dynasty and select 12 top teams. Then Simulate the season. Make a note of who your higher teams are, (ranking wise) and then go into the offseason. Simulate all of the tasks before Signing. Maneuver through the options until you see top rated recruiting class. If this is one of your teams that you selected then just switch to make them your active team. LB I believe is the way to do that. And then continue on past the signing task and the achievement should pop for you.

NOTE: You have to have the top team as your ACTIVE team, not just one under your control.