Reprioritizing a list of tasks automatically

[bluphoto]

I have a list of tasks numbered 1 to 10. they have differing priorities from 1 to 10, but the priority is NOT linked to the task number...
for example:

task priority
1______6
2______2
3______3
4______1
5_____10
6______8
7______4
8______9
9______5
10_____7



If I come along with task 11 and give it priority 5, then the task which had priority 5 now has p6; p6->p7, p7>p8 and so on. Similarly if I take task 2 which has p2 and change the priority to p8, then the tasks which had p3,p4,p5,p6,p7 & p8 all move up one priority point.

How do I get excel to manage these priorities for me?

thanks
Guy