Keyboard remap: enter to alt

I've succesfully replaced the top case of my MacBook Core Duo. The new keyboard has two <enter> keys (as did the old one), one in the 'normal' spot and one immediately to the left of the arrow keys. On the other Apple keyboards I know, this is the place of the left <alt>/Option key, and consequently, I've become very accustomed to have it there (for example, moving between spaces with <alt><arrow> is very easy and quick this way). Is there any way to remap this secondary <enter> key such that it behaves like <alt>?