A lot of customers want to know if you can upgrade from SharePoint Server 2007/WSS 3.0 to SharePoint 2013. The answer to that question is not directly. You'll have to upgrade your content and service applications(if required) through the process to get to 2010 and then to 2013. If you don't want to do the double upgrade (I know I wouldn't), you can look to 3rd party vendor migration tools. A lot of them will take care of this for you, for an added cost of course. Don't get scared off by the idea that these tools cost money, because people and time cost money too.