Well in case you havent got a better answer (and since I said I would) here's a quick run through.
Add unit with editor and set icon (I assume you've done that) take note of what icon number
Add name under civilopedia entry i.e. PRTO_Tigertank (same name as your art\unit designations- I've found there's less hiccups if it has no spaces)
Thats it for the editor except that you should set up the unit so it can be built immediately.
Make copies of the text files you're gonna change (see below) -JUST IN CASE-
Open 'PediaIcons' with any text editor (double click), word pad is fine
Scroll down and duplicate the last entry under units which is normally
#ICON_PRTO_Privateer
art\civilopedia\icons\units\65privateerlarge.pcx
art\civilopedia\icons\units\65privateersmall.pcx
and change the
duplicate to
ICON_PRTO_Tigertank
art\civilopedia\icons\units\66tigertanklarge.pcx
art\civilopedia\icons\units\66tigertanksmall.pcx
(assuming your tigertank icon is #66)
now the end of your units should look like this
#ICON_PRTO_Privateer
art\civilopedia\icons\units\65privateerlarge.pcx
art\civilopedia\icons\units\65privateersmall.pcx
ICON_PRTO_Tigertank
art\civilopedia\icons\units\66tigertanklarge.pcx
art\civilopedia\icons\units\66tigertanksmall.pcx
#End Units
You dont
need to add any comment to the civilopedia. Just dont click on any link to it while you're playing. If you want to add it just scroll down to units in the civilopedia text file and copy and paste all the text for i.e. panzer- watch that you keep the correct spacing between the units etc - change all 'panzer' text to 'Tigertank' and alter the duplicated text as you see fit - .
Its actually pretty easy

I hope it works for you.