Purchased TV shows but can't sync them as Ipad is linked to another computer

I have purchased quite a lot of TV shows this Christmas on my iPad2 but when I try to sync to back it Up on my PC I get a message saying the ipad is authorised to another computer and I would have to wipe it and then sync. I could get hold of this old computer and de-authorise it, would this do the trick without me wiping the ipad? I don't want to lose all the TV I bought!! ( totally forgot that since I last synced the ipad I have bought a new computer and given the other one away!)

But

Before I do this there is music on that old computer that I need to get off so somehow then need to merge 2 iTunes libraries which are linked to one account (I used an external hard drive).

What do I do for the best without losing everything?