Explanations / Notes:
Group by: System is the default, and what you pick to look at the numbers for one system. Hardware Family is for the sum of various versions of hardware: choose DS with it to see the sum of DS and DS Lite. Manufacturer is for when you want the sum of all of one manufacturer's systems.
Famitsu data goes back to the beginning of 2000, Media Create data goes back to the beginning of 2002. If you request a week that goes back further, it will start with the first week with actual data.
Famitsu's WonderSwan data is a bit goofy. It begins with WonderSwan, eventually introduces WonderSwan Color and Swan Crystal listed separately, then combines them all back into the listing for WonderSwan.
Setting a YMin without a YMax makes for a less accurate cutoff point due to the way JpGraph works. Luckily, this seems something that would rarely be done.
See an expanded calendar here to better match up weeks of various years at arbitrary points.