Crystal Reports Help me in the Report design-Monthly expenses

Message

   Hi 
i am using CR XI.
i have a table in oracle Tab1 having column Invoice Date and amount 
user will input from date and to date as parameter.

i want the sum of the amount month wise 

i want in my report  like this

supppose user selects Jan/07 to mar/07

report should look like below

Prior month        sum prior month exp        current month      sum current month exp

Jan/07                   100                                feb/07                    200

feb/07                    200                               mar/07                    300

Please help me to design this report.