How do I Sync iPod/T to iTunes when iPhone is 'Master'?

Question

The Situation...
I have a new iPhone 4S synced to iTunes on my Mac.
I have an old iPod Touch which was synced to a PC on its own iTunes some years ago but I have not synced it for years to anything.
The iPhone is synced under one identity, the old iPod is synced on an older one of my identities.
What I want...
To sync the iPod Touch with my Mac using the same identity as for my iPhone.
To get the same iTunes library currently syncing to iPhone to appear on the iPod Touch, i.e it is a perfect mirror or copy on both devices.
If I purchase a downlaod to play on iPhone - that it then will play on iPod Touch after I synced it (the Touch)
Do be able to do this without a convaluted complex preocess which takes hours of my time, and without any special additional software
Your Help?
Is this even possible?
How can I do it quickly so t works without messing up my iPhone?
Thanks in advance for your suggestions...

Answer 1

What is the risk if I follow your sugestion, of me losing data on my iPhone or iTunes?
None.  I used to do it with my 3G iPod Touch and iPhone 4
I understand that my Touch is pre 'iOS' and is back on whatever old 'version 2' is or something like that.
Will the Touch be able to take all this data from iTunes given its old operating system?
It will only sync what content it understands and can work with.  The rest will be left alone.
Cold I not just instead create a special 'playlist' on my iTunes dedicated to this Touch (for another reason too - my Touch is only 8Gb and my iPhone is 32Gb!). What I am scared about is what happens when I pulg in my Touch to iTunes for the first time.
That's definitely one way of doing it. Perhaps this article will be of assistance.
How to use multiple iPods, iPads, or iPhones with one computer
So what will I see on my MAc iTunes if I just plugged in that old Touch?
Your iPod Touch will appear in iTunes.  iTunes will notify you that it must be erased before it can sync with the new iTunes library. So go ahead and let it Erase and Sync.  Even if you do set up the iPod to sync different from the iPhone it will have NO affect on your syncing preferences and such for the iPhone.
I think I set that Touch up on iTunes on an old PC years ago under a dfferent Apple identity you see - so what shold I see and what should I do when I (if I) pluf that Touch in to my Mac iTunes?
See above post.  It doesn't matter it was used on a different Apple ID previously. 
In short, just go ahead and plug it in to your new iTunes library on the Mac.  Take your time and read any prompts that appear.
B-rock