You can create your own party using the multiplayer option which is handy if your goal is to create the ultimate powergaming party.
But in my opinion, by doing that, you miss a whole lot of witty interactive depth and banter which goes with finding the NPCs to make your party. With the original BG for instance, you'll find there are 25 NPC's alone to choose from at various stages of the game, each with their own idyosyncracies and thoughts.
I mean the first time my party members ever had an in party argument in BG, it was just too hilarious for words. A truly great feeling.
Admittedly with IWD's party setup, I didn't mind so much since it was reflecting back to the ol' Goldbox AD&D way of party formation, but I did miss the npc interaction which is one of the virtues of the Baldur's Gate series.
I can also reccomend what Dace said about going from the start of BG right to the end of II by importing your character. Its a very epic feeling. I'm currently doing that with my Avenger (which is seemingly quite the popular class around here lately) and have just nearing the end of Chapter 5 in BGII. I think i started BG back in early November, December last year...and yet I've still so far to go.
Anyway, all the best with your travels and endeavours to find the original game.
Cheers,
Cerebrodragon