Create a running total field that counts the records. Then right click on the details section of the report, and select format section. To the right of the Suppress checkbox is a button labeled X-2. This is the conditional format area. Hit that button and enter a formula
Remainder({#countfield},2)=0
This will suppress all "even" records. Alter the formula to get the odd ones, or maybe tie in a paramter even/odd? field and put the proper logic in the same area, conditionally suppressing the records as you see fit.
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