If you are new to Windows Embedded CE you might want to get a trial version. There is a problem though: Platform Builder (the tool to build CE kernels) is a plug-in to Visual Studio 2005. So to try building a CE 6 kernel, you need a version of Visual Studio 2005 (actually you need even more because you will have to install VS 2005 SP1 and a patch if you are using Vista). But Visual Studio 2005 is not available in eval version any longer on Microsoft Download Web Site.
You can still order the eval DVD of CE 6 that contains an eval version of Visual Studio 2005. But if you prefer a downloadable version, then here is a solution to get download links to all the elements needed to try CE 6: http://msdn.microsoft.com/en-us/embedded/bb961981.aspx