Do I need to play IWD1 to get IWD2?
When I say need I mean would it be useful for plot purposes. In baldur gate, BG2 followed directly the plot from BG1. So much so that the BGT project actually merged them into a single game. (using work from the TUTU project which ported BG1 to BG2 engine)

anyways, is the IWD2 plot a direct continuation of the IWD1 plot? or is it like NWN where NWN2 has absolutely nothing to do with NWN1?

Thank you for clarifying. Same world, different people... mmm, I can live with that. I think I will play IWD2 firs than. ouch, then why even bother playing a game this old if its so barren of plot? There are dozens of NWN modules I haven't played yet with far more expansive plot than this...
I hope you were grossly exaggerating.

It's an exaggeration, yes, but the IWD series is closer to a dungeon crawl than plot-heavy. That's not to say there isn't a story, but it's not a deep one like Planescape. Why play IWD? You create a full party and the combat is a lot of fun. The story is decent.

No, not really. Both games are mostly hack 'n slash anyways, and story isn't the reason to play them. Instead, they offer a much more pure dungeon crawling, tactical enemy murdering, loot grabbing experience.

You are perfectly fine in playing IWD2 first, although I am playing through the first one right now and it's no slouch either. It's really just what ruleset you want to be governed by.

There's a lot of story in IWD, but you don't need to know it for playing IWD2 since it happened long ago when your party members (at least the races which don't live hundreds of years) weren't even born.