Well here's my root tree, using Slackware 10.
vince@box:~$ ls /
bin/ #stores programs
dev/ #contains devices (everything in linux is a file, even devices, processes, etc.)
etc/ #mostly setup files for other programs (I think...)
include/ #function libraries
lost+found/ #
opt/ #auxilliary packages
root/ #the root user's home directory (root is all-powerful master of the machine)
src/ #sources
tmp/ #temporary file storage
var/ #
boot/ #
doc/ #
home/ #contains users' home directories (other than root)
lib/ #function libraries
mnt/ #default point for mounting devices -> hard drives, cd-rom, etc.
proc/ #processes (processes are fiels too!)
sbin/ #shared programs
sys/ #sytem stuff
usr/ #
This is a quick explanation (probably erroneous, too...).
Check this page for more, complete, accurate information:
http://www.freeos.com/articles/3102/
Good luck with the transition!!!!
vince