The easiest way to create a .sis file would be to use the tool makesis. You can download the tool from here:
http://www.kmdarshan.com/makesis/Makesis_v1.0_by_Gip.rar

http://www.kmdarshan.com/makesis/Makesis_v1.0.zip

Also you would need to download this dll, and put it in your C:WindowsSystem32 for this tool to work. you can download the dll here:
http://www.kmdarshan.com/makesis/Comdlg32.zip
good luck packaging.