go to this link..
http://freearc.org/InnoSetup.aspx
and download Version 4.0 script by shegorat.
it's basically a simple freearc script for decompression, which can be implemented in simple wizard form from inno setup enhanced edition, plus you can use your own style by applying cjstyles or your own style..
if you want ready made scripts go to ultra-arc section of this forum, you can download rg mechanics, blackbox, windowsphone etc. there on first page.