why do some characters gain more experience than others,i've just started BG and Jahira gained alot more experince than my main character she leveled up with 2000 exp and my main character (a mage) only had around 1000 is this supposed to happen??

This is because when you add the NPCs to your party for the first time, they are automatically given an amount of xp, to make them fit in your party (it would be silly that you are level 6 and you get someone to join you with level 1). That xp isnt exactly the same as you have, thats why she has more than you. Also, when you get xp for a killing or a quest, the xp cant be exactly divided between your party members, for example 1000 cant be divided between six, so some characters gain a little more xp than the others (normally the top characters are asigned more xp than the last ones, when i say top and last im talking about their position in the right bar of the screen)

------------------
http://www.angelfire.com/anime2/memnoch/ertai2.gif "I don´t want to be alone anymore. Angel, have you forgotten me?" -Ertai, Captive of the Blinding Angel

Well, Ertai, there are some circumstances. If you play through BG1 a second time with the same character, NPC's are around level 3, while you're at level 8 or 9. Also, more experience is rewarded to the character that slays the opponent.

Nanobyte, i didnt know that about the second time, ive never used a character more than once.

About the xp, im not sure, once we had a debate here. Lets put an example: you kill a diseased gibberling, worth 7 xp, with your 5 member party.

Theory #1: the first and second characters gain 2 xp, the others gain only 1.
Theory #2: all gain 1 xp except the killer who gains 3 xp.

I really dont know which one is true, or if it isnt neither way. Any help ?

------------------
http://www.angelfire.com/anime2/memnoch/ertai2.gif "Sigh" -Ertai, Captive of the Blinding Angel