From "High-Tech Dictionary":

Leap years fall on any year that either can be evenly divided by 400 or evenly divided by 4 and not evenly divided by 100.For example, the year 2000 is a leap year, but 1900 is not.

From "Cisco Year 2000 Compliance Definition:"

Leap Year occurs in all years divisible by 400 or evenly divisible by 4 and not evenly divisible by 100. For example, 1996 is a Leap Year since it is divisible by 4 and not evenly divisible by 100. The year 2000 is a Leap Year since it is divisible by 400.