Win32DiskImager (find it at http://www.raspberrypi.org/downloads) is the tool of choice for plopping a Raspbian image onto an SD card and it works perfectly. Unless the card has already been used once for this purpose and you want to reuse it with a new version of Raspbian – in which case Win32DiskImager will cough and splutter and refuse to do it.
What’s happened is that, as part of the process of adding the image, much of the space on the SD card has been made invisible to Windows. This is why, if you try to reformat it using the built in Windows tools, you’ll end up with only 70MB or so of apparent space.
What you need to do is restore the SD card to its original state and to do this, you need to download and install SD Formatter for Windows. Run it, select your SD card and you’ll see it report the incorrect, smaller size. Click the Option button and select Full(Erase) from the “Format Type” menu and, critically, select On from the “Format Size Adjustment” – click OK to close the option setting box and Format to format the SD card.