I dont think u can switch goalies...

When you are playing a game, make sure you can change/edit the lines, select manual instead of auto, when you arent playing the game, just move the goalie you want to the top while editing your lines

In NHL 07 you actually cant switch goalies during a game (maybe you can if your goalie gets hurt, but I dont even know if thats possible). All you can do during a game is pull your goalie for an extra attacker. To do so, at any point during your game just press the Start button to bring up the pause menu. On the pause menu the fourth option will be called Pull Goalie, or something to that effect. Press X on this option to take your goalie temporarily out of the game. To put him back in the game just follow the same steps.