Separating Positive And Negative Numbers

I have a field on my report that contains positive and negative numbers. I'm trying to find a way to Sum the column twice for two different fields (one for positive sum and the other negative) To make this easy let me give a small example with explanation of the issue I am having. 14 rows of data containing positive and negative numbers in a field called [Rooms]:

1) -1
2) 1
3) 1
4) 1
5) 1
6) 1
7) 1
8) 1
9) 1
10) 5
11) 1
12) -5
13) 1
14) 1

The positive numbers represent confirmations, the negative numbers represent cancellations. I need 2 fields to separate these. The first field's control source is Sum([Rooms]). No problem there. Access does the math and comes up with "8" confirmations which is correct. Then in the second (Cancellation field) I try something like Sum([Rooms]<0) to get the negative numbers which should add up to -7 (-1+-1+-5), but instead I get -3 because it's not summing the values, it's really returning the number of rows that has a negative number. Is there any way this can be done at the ControlSource Property of a report field? Or if I could do a "Where" clause in a ControlSource I could acheive it another way, but I don't that is possible. Is this just something I'm missing with the way I'm stucturing the ControlSource or is it not possible. Or alternatively, is there a way to separate it in the query and have a separate query field for positive and negative going into the report. I can do one or the other in the query but I can't seem to do both without showing values of each type in both query fields.

Thanks for your help!