Some years back I had found SisWare, a ideal tool for analysing the sis packages. Today, while searching some sis installation error code resolution I found another great tool for sis packages creation,editing and unpacking. Its called SisContents and developed by a russian developer. The tool is awesome and has features to see the executable details and as well as resource files.
The best part is that its freeware. It also supports .dm packages as well ;).
Here are some of the screenshots of SisContents in use.
I strongly recommend this great tool and if you appreciate the great work done you can make some donations to its creator as well.