I would have my data in one big table, then you can use sumifs to match the mileage amount to the start point column, and the end point column
start finish mileage point A point B 100 point A Point C 150 point A Point D 200 point A Point E 250 point A Point F 300 Point B Point A 101 Point B Point C 151 Point B Point D 201 Point B Point E 251 Point B Point F 301
Date start point end point mileage 8/1/2011 point a point b 100
formula for mileage is =SUMIFS(C:C,A:A, f2,B:B, G2)
where c:C is the column containing the mileage numbers, a:a is the start points, B;B is the finish points in the data, and f2 is the user entered start point, and g2 is the user entered end point (has to match perfectly to work)
i would use data validation on a named range of all the location gchoices to create a pull down list that way you know that it`s actually going to match the data.
you can use the indirect formula to make it look in seperate tables if you don`t want to merge all the data into one place.
i think sumifs only works in excel 2007 or better.