I've got a couple questions. where should I start to read, I'm looking for when Dick Grayson (for whatever reason that is unknown to me) leaves Batman, drops the name Robin and becomes Nightwing. Which issue/series is that? And if I start reading Nightwing new 52, and read comics of nightwing pre 52 will that get REALLY confusing? Also which issue/series is it when Dick takes up the mantle as Batman temporarily?
You could start with Nightwing Year One. Thats where I started with Nightwing. It chronicles his fallout with Bruce and subsequent transformation into Nightwing in that 6 issue story arc. However, the trade for this is currently out of print, at least it was when I tried to pick it up. So you'll have to hunt down the back issues (Nightwing #101-106)
I believe Judas Contract 11 was the first appearence of Dick as Nightwing? If you want his current origin story you need Nightwing Year One. The first time Dick filled in for Batman was the Prodigal storyline(mid-30s in Batman: Shadow of the Bat and 510s in Batman). If you're looking for more famillar post-Final Crisis BatDick, the first issue is Batman 687. Most of what was canon pre-New 52 is still sort of cannon right now, so you should be fine reading old stories as long as you take major events with a grain of salt.
@aurum19: It might be a tad confusing to read both series, yes. The New 52 is somewhat retcon-happy, so I'm sure reading the two side-by-side will elicit some mighty "huh?" moments. If I were you I'd just pick up the Grant Morrison Dickbats stories (there are three trades, starting with Batman & Robin Reborn) and move right into the New 52 from there.