About MyBook Studio Edition II

I recently bought an external hard disk MyBook Studio Edition II for my iMac desktop. I had followed the instruction on the link below

How to install, partition, and format a WD drive on Windows (7, Vista, XP, 2000) and Mac OSX

to make partition for my XP OS and Mac OS(My computer has 2 OS) . So, I suppose I can open my file in my external HD from XP OS or Mac OS side. But when I opened XP OS, window cannot detect the external HD. Then, I go to my computer–>manage–>disk management and make partition using all the space in the External HD. Then I try to open the HD but it need to be formatted. So, I scare that I will formatted all the Mac file inside. Then I go back to MAc OS and open the External HD. But in result, Mac cant detect the external HD.

(Priority)What should I do to save all the files? Or can I format first then find data recovery software for MAC to recover all the files in MAC OS?