Summing values based on a dynamic date range

I have two lists (see enclosed file) that will keep growiing as time goes on.

On the "Summary2" page i basically want to calculate something based on the a start and stop date.

in the example the start date is 6/1/11 and the stop date is 8/1/11.

I want to calculate something based on the start and stop dates for a list that i guess is dynamic in that it keeps growing with time.

Any ideas on how to do this without using vba macros.

I don't quite understand your sheet.
Why are all your dates the first of the month until May'11, then they are the end of the month?
This doesn't seem to fit with the result you are expecting in B4, based on the dates in B2:C2.

You seem to have PartA derived from a percentage of the total.
Should this not be that PartA/Total gives you the % met, as your calcs in B4 & B5 suggest?

Try this in B4

=SUMIFS(Summary1!C:C,Summary1!A:A,">="&$B$2,Summary1!A:A,"<="&$C$2)/SUMIFS(Summary1!B:B,Summary1!A:A,">="&$B$2,Summary1!A:A,"<="&$C$2)

"<=" might have to be "<" if the date in C2 is meant to be 1-Sept-11