How to transfer data from NEW mac to OLD?

I want my Macbook Pro, gotten around early 2009 (runs on Leopard), to have the same things on it that my newer iMac has (runs on Snow Leopard). However, I'm running into a problem when I try to do that.

A few months ago I had no problem transferring ALL my data, accounts, files, applications, etc, from my new Mac to my old Macbook. I had erased the disk on my Macbook and then somehow managed to transfer all my data from the new Mac to the my old Macbook from a Time Machine backup.

Now, however, when I try to transfer it now through Migration Assistant or the startup disk, my Macbook tells me that I can't because my Macbook runs on an operating system older than my new Mac. It will not allow me to.

I don't remember how I did it last time. I remember getting the same error message, but finding a way to fix it... but I forgot completely! Last time, using the same Macs, and the same situation, I was able to transfer my data from the new Mac to the old one using Migration Assistant and Time Machine. Now it won't let me.

Is there any way to do this?

Please, advice would be appreciated. Thank you.