Put the card in that you want to trade TO and load the game from it...go to the garage and then select "Trade" and then insert your friends card into slot 2. When it prompts you to load a garage select the memory card slot 2 and you'll see his garage. NOW...you have to have the MONEY to buy his car or cars that you want...and the are at the high $ numbers!!!
If you want him to be able to buy from your garage...then load his game from slot 2...and then select trade...and when it prompts select to load the garage in slot 1 (yours) and again HE must have the money to buy the cars from you.
It's not really trading as much as it is the chance to BUY cars from another memory card.
As for replecating your cars...I've know that trick for a while too...I have a memory card called "the garage" (actually 2) full of cars of all colors and fully upgraded that I buy them from...easy that way.
4 "Bullocks#999",
