Year on Year Comparison by Month

[Revelator80]

Hi,
I am trying to build a report that shows, by month, the comparison to last year's figures so:

     April       ||      May      ||     June
--------------------------------------------------
2009||2010||2009||2010||2009||2010
--------------------------------------------------
10   || 20   || 20   || 10   || 10   || 20 

My data source is a Transformer Cube and I have played around with parallelPeriod etc. to create two Data Items for the selected year (from a prompt) and then the year before that. What I can't do, however is format it into the above example - whenever I try it only pulls back one or the other so the issue musy be in relating the two sets.

Can anybody advise?
Many thanks
David