What is the difference between them? My character has a BAB of 4 and an attack bonus of 6. When calculating the attack role (melee) you D20+bab+strength modifier+size modifer to determine if your attack is greater than the enemy AC. So what does the attack bonus do?

BAB is the attack bonus only from your character levels.

AB is BAB + all your other bonuses (Str + Weapons bonus).

AB + D20 gives you are score to compare to enemy AC.

Thank you very much for clearing that up! Apprecite it friend!

To expand a bit on PeterScott's answer, each character class in 3rd edition D&D (NWN 1) or 3.5 edition (NWN 2) is classified as having either high, medium, or low progression of base attack bonus (BAB). Classes with a high BAB progression gain +1 BAB per character level in that class, such as fighter. Classes with low BAB progression receive +1 BAB per two levels, with the bonus granted on each even numbered level (e.g., mages). Classes with medium BAB progression receive no bonus on the first level and every fourth level thereafter, but a +1 bonus on each of the intermediate three levels. Clerics are an example of this.

So if you are a fifth level fighter, you have a BAB of 5 (one per character level). If you are a Fighter 5/Cleric 1, the you still have a BAB of 5 because the Cleric class receives no BAB increase at level 1 (irrespective of when the level in that class is taken). A Fighter 5/Cleric 2 has a BAB of 6 (+5 from fighter levels, no bonus from the first cleric level, and +1 from the second cleric level).

As PeterScott explained, your overall attack bonus (AB) is your base attack bonus plus or minus any bonuses or penalties accrued from statistics and weapons. Your AB is what determines if your character can hit an enemy with a particular armor class (AC).

Thus, if you are a 5th level fighter (BAB 5) with a 16 Strength (+3 attack bonus) that wields a +1 longsword (+1 attack bonus), then your AB is 5 + 3 + 1 = 9.

If you are a 4th level Wizard (BAB 2) with an 8 Strength (-1 penalty) wielding a regular dagger (no bonus), then your AB is 2 - 1 = 1.

Thanks man this helps a lot. I like too understand the math behind the scenes.

I'm gonna post another thread about NWN 2 and XP unless I can get an answer here. My question is: is NWN 2 like Baldur Gate in which XP is divided between party members or do you get the same amount of xp after an encounter or quest if you were solo or in a party?

http://nwn2.wikia.com/wiki/Experience_point

I believe what they mean by "sometimes" is that it depends on how the encounters have been designed. The larger party will spawn greater numbers of creatures so, in theory, the amount of XP lost per kill can be offset to some degree by more kills.

But when they do not choose to use encounter triggers (i.e. pre-placed hostiles or spawn points), the total creature count has no way to scale. Penalty is typically around 10-15% less per party member and that includes summons, familiars or animal pets... anything showing up on the party list. With higher CR types, the percentage reduction will approach the standard percentage. With low CR, the rounding down in XP points due to fractions of the percentage can increase as high as 25% penalty (IIRC).

Quest rewards are generally immune from XP reduction.