Nice triple post.
I haven't taken a look at the older books for a while, but currently the "Thief" role is played by the Rogue class. So I guess you're father could have been a rogue that was a thief....
As to Nick, the books can be bought pretty much anywhere you can buy books. Unfortunately all they really sell now are the new 4.0 books. I personally prefer 3.5 which is now available only through ebay, amazon, and specialty stores.
Neverwinter Nights is a videogame based off of DnD. I haven't played it myself, partly because you have to pay for it...
If you want to play a DnD mmo, try googling "DDO". It was okay but again I much prefer the actual game.