You can unlock the teams (like the 85 bears) through the madden cards.
I never really used the Madden Cards, I just got frustrated because some people online can boost their player stats with cheats that let them use the cards (so I started finishing the achievements).
Pretty much, you do some things on the list of achievements (by the madden cards). Like Intercept a pass on def. Tackle a player 3 times with the same guy etc. And you get points.
With the points you can buy a pack of madden cards and they have all the goodies.
The messed up thing is, some people say the cards are all random. But you will get better cards when you complete more difficult tasks (for some reason if you do some amazing things to get your points your cards will be awesome!) If you just get a pack though from a normal collection of points most of the time you will get a bunch of duplicates or player cards for people on teams you probably wont use (like the browns).
It is semi random, so all it takes to get everything is buying a massive amount of cards. But you can get the cool stuff quicker by doing things like returning int's for td's or sacking the qb in situations that are imparitive (like 3rd and short 30 seconds left of the game and both teams are tied up).
You can also cheat, like all the losers that cheat (but your no loser! So don't cheat), with simple things like hooking your pc up to your ps2 and using a certain piece of software to access and modify a feed. Or modifying your memory cards save file by using one of the many programs they have on the net, or using your psp to download the save. And or game shark.
But it costs money to do the other things. And your integrity.
man is continually revolting against an effect, while all the time he is nourishing and preserving its cause in his heart