My C skills are nearly null. I can patch and hack very simple stuff and do a few config and compiling tricks. I do lots of stuff in shell using Xdialog and other such tools.
Some time ago I did a one-line hack to PDV to make it use gzip instead of compress. It can also be made to use bzip2(at least). What it does is let you create a self extracting archive which can show a license, a message and/or run a script or program on completion. This also what freewrap does, except that it contains a statically-linked binary of tcl/wish. When you create the package you write the tcl script which makes the GUI installer.
I see now how to do the same sort of thing using pdv with an included binary of Xdialog, greq, gtk-shell or other such GTK program. You could also use newt/whiptail.
The hard part is how to make a system which makes it easy for the user to create various types of installation handling routines. Some programs will need sevearl routines for config files and paths, etc. Others could simply be installed to the system.
What kind of software are you talking about? Binary or source packages, single-file scripts. Universal packages which figure out what system they are unpacked on a install using the tools appropriate to the distro? Are you wanting to do a C or C++ program, or what?
See here for some of the tools I use(also one dir up):
http://distro.ibiblio.org/pub/linux/...nts/MsgDialog/