It's a Panasonic model and according to this page it can burn & read DVD+R DL media:
http://burners.burn4free.com/matsushita-matshita-panasonic/matshita-sw830.htm
I've been unable to verify that with the manufacturer though since I can't find manufacturer's page for that model.
You can buy DL media as a single disc in some stores, so maybe buy one and try it before buying a pack.
Make sure you buy the '+' media (DVD
+R DL),
not DVD-R DL.
Also remember that, although Windows 7 supports dual-layer media, it can only burn multisession discs. So if you want to avoid multisession burning you'll need some third-party burning software.