Ceppo, here's why your calculation seems contradictory:
An hour is divided into sixty minutes.
A degree is divided into sixty minutes.
The two sorts of minutes have the same name, but are unrelated.
The "1 minute = 1 nm" rule applies to minutes of latitude. For every 60 nm north or south you go, you move through an arc of about one degree on the Earth's surface. This is approximate, and it only works in the north-south direction. (It works east-west at the equator, but you probably don't live there).
Your 1 hour = 15 degrees observation is accurate with respect to the rotation of the earth. The earth makes a complete 360 degree rotation in 24 hours, so in one hour it rotates through 15 degrees.
Neither rule can be used to calculate the distance from London to New York. If you still want to do that, look at the Great Circle site suggested.
[This message has been edited by Luftwaffle (edited 30 August 2000).]