It will tell you right on the tab if it requires a license. (since you have a 410 it probably does) they seem to be priced reasonably. If it is NOT telling you that you need a license and it is jut blank, then you need to turn it on using the Snap Extensions tab at the very top right hand corner of the page (Fourth tab over) It will tell you if it is enabled or not. If not click on the name which will bring you to a screen asking you to enable it.
If it is not licensed then you can purchase it from
http://www.cdw.com/shop/products/Gua...e/1061938.aspx
or
http://www.snaphq.com/iSCSI-Software.asp
The second link gives a better description, and I know it isn't in the list but if you are working on a mac, the Globosan initiator also works.