Bare in mind I am also new to IA (just played first campaign mission), I have also bought Descent.

I have looked at the rules but I am very concerned starting two games at once will 'confuse' the rules round from game to game.

Can anybody advise, looking at the rules for descent, am I right in saying its basically played the same way, just with different looking tokens and cards, (different turn system too with each side taking a go then the other for the full turn)...but essentially, same game system?

I plan on setting up the first 'tutorial' campaign this week to try it out with me as overlord vs my wife playing the heroes, the wife has grasped IA very quickly but scared of putting her off if she has to learn two systems.

There are a lot of more subtle differences than the ones that you mentioned. Check out this link. I am not sure if this list is complete.

Frankly, I am not sure if it is a good idea to try to learn both games simultaneously.