The most efficient way to find position of a returned row relative to the total number of rows?

[eluser]Dandy_andy[/eluser]
Suppose I have 100 rows in a table and each row has a value/column X which varies for each row. How can I found out what position a particular row is relative to when ordered by X? I am looking to do this so that I can output a position value based on the total number of rows ordered by value X. Is there a simple way to do this using the active record class and bearing in mind the number or rows will increase as entries are added?

Any help appreciated. Thanks in advance.