I recently got into both Warhammer: Invasion and The Lord of the Rings: The Card Game and now I am considering A Game of Thrones (why yes, I am crazy)...

I just found out that this used to be a CCG and then switched to the LCG format. I'm curious as to how the CCG and LCG interact. Can the old CCG cards be used with the LCG? Are all the old CCG cards available in the LCG packs?

Being somewhat OCD about making sure I have ALL of the content for games I buy I really don't want to have to go searching for old AGOT CCG cards if they are not available anymore but are useable with the LCG.

First, yes, the CCG is compatible with the LCG. That said, the vast majority of CCG cards are not legal for tournament play. Some, but not (probably) most "friendly game" players do not use them anymore, as they tend to be overpowered compared to the LCG. Some of the CCG cards have been reprinted for the LCG.

That said, we do use CCG cards (at least the ones that look similar to the LCG) in our games. It only took me a few months to get the cards I needed, including Rares (although I still need a few Promos to finish).

Hmm, so if I were to only buy the LCG packs, would we be missing out on much? I highly doubt I'll ever play in any tournaments. I tend to just play with friends.

"Missing Out"? That depends. There are over 1200 cards in the LCG, and another Chapter Pack (20 different cards) comes out this month. Then the Lannister Expansion (55 different cards) comes out soon, as well...

Buy the Core Set and play it with your friends. Then come back and ask the question again :-)