Basically, there are 4 offensive and 4 defensive tactical dispositions that can be "turned on".
The offensive tactics can be called during the match by pressing the keypad 2,4,6,8.
When pressing keypad 8 the Counter Attack option is on. This means your strikers will move quickly forward once you have the position of the ball. Look for breakaways with long passes.
Pressing the keypad 6 sets Wing Play on. This means you wingers (left and right midfielders) will be on the flanks and the attackers will move away from the penalty area when you passing the ball in the flank. This is good for setting crosses or penetrating the penalty area from the sides.
Pressing keypad 2 is the Box Offense. With this option on, all your attacking players will move towards the center of the front penalty area border. This option is good if you want many players inside the small area of the field. Actually, I do not like it, as it always draws many defenders to the area as well.
Pressing the keypad 4 is the "3rd Man" option. This will cause you defensive midfielder (or the one that is left behind during the attack) to join the attack from behind. This is very good potential for a long-range shots (if you are good in this tricky aspect of FIFA08) or just another attacker with penetration passes.