Install DVD ripping software on your computer. SanDisk offers a free download for this purpose, the Sansa Media Converter (see Resources).
Once you have the converter installed, use it to rip the DVD to one of the supported formats: MPEG or WMV, for example
Connect the Sansa to your computer using a "30 pin" cable from the device to your computer's USB port. The Sansa comes with this USB cable, but if you do not have one, see Resources for where to buy this USB cable.
Click on Sansa Media Converter.
Select "Add Media" from the options at the top.
From the options, click on "Video." The DVD content will be added to your Sansa.