How to loop this

I have this this setup in crystal

if isnumeric(mid({ServiceInfo.SvcFrequency},2)) then
{ServiceHistory.ServiceDate} + 7 * val(mid({ServiceInfo.SvcFrequency},2))
else
0

My problem is I want to specify a stop date. Now is there a way to look at that formula and repeat it over and over to a specified end date?
Such as
So if the last service date was 1/1/07 and the freqency is w001(every 1 weeks) then the next service dates would be
1/08/07
1/15/07
1/22/07
...
...
Specified end date

And it would display every date that the service occurs on the report?

Thanks.Anyone? Please