The problem with the iscan source is that it heavily uses C++ for library and patches to the source is needed.
I have attached iscan.mk to start with. For more instructions how to build this visit http://trac.nslu2-linux.org/optware and wiki on www.nslu2-linux.org
When you wil have workable version you can post me to include it into optware. I am watching this thread so we can stay in touch here.