You can embed an XSLT file into your DLL, it then becomes a resource.
In the solution explorer select the XSLT file and in the properties change it from "Content" to "Embedded Resource" to get it included in the dll.
If you have an XSLT file called "myXSLT.xslt" in an the root directory of an assembly called "Namespace.dll" then the following code will load the transform:
System.Reflection.Assembly assembly = System.Reflection.Assembly.GetExecutingAssembly();
Stream s = assembly.GetManifestResourceStream("Namespace.myXSLT.xslt");
XmlTextReader reader = new XmlTextReader(s);
XslTransform t = new XslTransform();
/- Sam Judson : Wrox Technical Editor -/