Let me not steer you down the wrong path. What you need to do is follow the post from the MSDN forum. That will give you a date to start from. You will then have to write your own CAML that adds to the selectcommand.
You will have to add an <And> clause when you are doing 1 & 2 mos. prior. Just so you know, the CAML is contained within the selectcommand on each of your DVWP's. That is what you'll be updating. You may be able to use the GUI to actually create the filter, but when I did this previously, I used U2U and the post above.
I would follow this approach to the "T". After you get the base query up and running from the MSDN forum, post your CAML here and I'll help you through it.
I'm thinking your other thread is directly related to this one. Is that the case?