One memory card and two players?
If you have one memory card and you want to play a 2 player game with your friend, place you card in slot one and load. When the 1st player loads pick a car and choose your options (e.g. manual/automatic), but the second player says no card present (or something like that), place card in that slot and try again. When loaded choose car and your options and play.
The easiest way to get lots of money later in the game is to race the qualifier for the all nighter. You get $20,000 just for qualifying and it is very easy to do this with the GTO special edition or any other car with good speed/acceleration and handling. It takes app. 1'45" to complete with the GTO special edition.