building slightly modified distro?

[David Feldman <mailing-lists interfacethis com>]

I'm interested in playing around a bit with the Linux (mostly GNOME) 
UI, and ultimately creating a distro with an ISO installer that I can 
try out on my friends. It will involve changing some defaults, 
including and excluding specific apps, and perhaps modifying some of 
the UI code. I think Ubuntu might be a good starting point, or possibly 
SUSE or Fedora. While I have a decent amount of development expertise 
I've never really done anything like this before, and in the interest 
of time I'm hoping to avoid modifying code unless I actively want to 
make changes to its behavior.

How would I learn how to do this? Where would I get the necessary 
materials?

Thanks and sorry if this is OT,
--Dave