I've find a way to duplicate cards on the xbox 360 version of FIFA ULTIMATE TEAM 2010, it works perfectly and it will give you 3 copy of the same card.
It also doesn't require a JTAG XBOX 360 because it use a glitch of this expansion (FUT).
I'll do it every day, so fell free to contact me whenever you want.

IT ALSO COST ONLY 10K (coins of course) EVERY 4 CARD that you want to duplicate (u'll give me 4 card and i'll give you back 12 card).
Its a long process because after the duplication I'll have to play an online match with every single card, that's why after i got your card you'll have to wait at least 24 hours before get the copy.

so here are the prices :

1-4 Cards = 10k
4-8 cards = 20k
8-12 cards = 30k
and so on

If you decide to do this glitch, contact me via PM with the name of the players that you want to duplicate, I'll tell you the information of the bronze card that you have to trade with your players + my club NA ME. Don't forget to add the right ammount of coins.

I'M GOING TO GET YOUR CARDS FROM 9.30 TO 10.30 GMT EVERY DAY, so please be ready to do the trade in this period of time.

IM NOT A SCAMMER THAT'S WHY I'LL GIVE PROOF TO AND ADMIN DUPLICATING FOR HIM SOME CARDS.

THX AND FOR ANY QUESTION don't esitate to ask.