How to make your own custom dist or custom ubuntu

I made a custom ubuntu distribution(ubuntu 10.04) with all these packages for electronics and electrical students  with all these packages installed in it....

1. texmaker
   kile
   lyx
   scipy
   numpy
   sympy
   gap
   maxima
   gnuplot
   xfig
   dr.geo
   scilab
   ocatve
   qtoctave
   Rkwrd(gnu r)
   emacs
   labplot
   electric-electrical cad
   gnusim8085
   gpsim
   gresistor
   gwave
   kicad
   ktechlab
   qucs
   piklab
   avrdude
   simulavr
   ngspice
   geany
   grass
   splat
   bluefish editor
   emu8051
   eric
   geda-gschem
   gperiodic
   Sagemath
   Geogebra

I used Remastersys backup tool for this ......
http://www.geekconnection.org/remastersys/
Its is simple for beginners to use the gui and for experienced users can use thecommand line you can akso take the backup including the userdata by using remastersys

Remastersys can be found in synaptic after adding this line in /etc/apt/sources.lst
# Remastersys
deb http://www.geekconnection.org/remastersys/repository karmic/