Can you explain step by step, as I'm sure you must be missing something?
I use win32diskimager and so I would
Download the file from http://retropie.org.uk/download
Use 7-zip to extract the .IMG file from the .gz file
Insert my SDCard, check I can see a drive on it. If not use diskmgmt.msc to check the card, delete old partitions and create a single fat32 partition.
Once I can read a drive in explorer then
Open Win32diskimager, select the file and the SD card drive letter to write to. Click write.
I'm probably over paranoid with regard to drive letter and partition checking. However, the reason I check the drive letter is that I have in the past accidentally imaged to a usb stick or portable hard drive by accident, doh! I once lost over 800gb of files including old pictures and videos as I wrote a Raspbian image to my external hard drive, not a pleasant experience .
Si