I'm supposed to be watching Who in order as well. I introduced my housemate to it and we started with An Unearthly Child*. I figured that watching additional episodes I'd already seen on my own didn't count as out-of-order.

*The strangest thing about it is that she has no idea about New Who. I'm used to that being common ground with pretty much everyone in fandom, regardless of their opinion of it.

And yes, The Invasion is wonderful and most excellent.