Always one I have to look up....but if you've got an xsd it's really simple to turn it into a class. Just use the xsd.exe tool. Options i usually use are: /c (to generate classes) /l:CS (class in c#) /n:somenamespace /o:outputdir
You can also use it to go the otherway, and generate a xsd from a class.
A simple example of using this can be found here.