[justbondage]

Maybe I am over simplifying this but....

Have your crons only function to be to update the niche flat files with a number that appears at the top of them $currentnum or something - this will start at 0 and go to the amount of links you have in the file, once it gets to totalnumberoflinks-1 it should reset to 0.

Then all you need to do is read in that number, read in the links as an array, then output the scalar that lives at array[$currentnum].

This of course is assuming you want each link to get am equal amount of exposure.