[plug] subnet tutorial

[Senectus .]

In my recently slack job I've not done any sub netting stuff in over 2
years.. I've recently realized much to my terror that I've pretty much
forgotten _how_ it works.
Does anyone know of a decent on line tutorial that I can run myself
through, one that someone might recommend etc..

Thanks 
:-(

-- 
Ubuntu Warty 4.10 (desktop)
and Hoary 5.04 (Laptop) (kernel 2.6.10-19 686)