Of course, if you are using SQL Server 2008, you don't need to use spherical approximations such as this - just use the inbuilt spatial functions:

Point1.STDistance(Point2)

STDistance() gives a more accurate result than the example here because it is based on an ellipsoidal model of the earth rather than a perfectly spherical model. Also you can use it to find the distance between any type of feature, not just points. (i.e. to calculate how close a route passes to a point, or the distance from a point to the edge of a polygon)...

http://www.amazon.com/Beginning-Spatial-SQL-Server-2008/dp/1430218290