Mad3: I have finished baldurs gate 1+2 and nwn2, but I am new to IWD.
About IWD1: Since this is combat heavy and your max lv is 14 or 15 (If I get the manual right) dual classing is not a good idea because you cannot use the abilities of your old class most of the game. As far as I know from bg2, dual classing means fighter7 or 9, then cleric, thief of mage.
As kmonster noted, dual classing can make a very powerful character. For that second thief spot, I'd maybe try something like a Fighter dual classed to Druid at level 3 or 7 (if you go this route, be warned that the character must have a 17 CHA and 15 WIS minimum), a straight-up Druid, or kmonster's suggestion of a second FTR/Thief multiclass.
Mad3: I thought of something like:
-Mage (is it right that the opposing shools changed with the expansion?)
-cleric
-Bard (What do bard songs in DnD2 do anyway and how do they get better with lvl?)
Check out
planet baldur's gate for Bard Song descriptions. The individual songs don't improve with more levels, but they can be quite useful. More info on the game itself and some of the mechanics in links to the left of the page I linked to as well.
Mad3: About IWD2: I made a guide for character creation in NWN2, so I guess similar builds work here too.
-one lvl rouge, rest wizard (scouting, kill enemy groups with fireball before they know what hit them and run and hide again if something survives.
- one or two lvl paladin (depends on when you get saving throw bonus and fear immunity in this game), rest scorcerer (killing things with magic)
-one or two lvl paladin, rest cleric (healing, buffing, some damage spells)
-ranger/rouge (classical dual wielding backstabber)
-bard/barbarien (fighting and singing)
-fighter/barbarien (brute force) or fighter with some cleric lvl (something like the warpriest in NWN2, brute force+buffs)
Again, as kmonster noted, it may not translate all that well from NWN2 to IWD2. A pure SOR is generally better than a Pally/SOR due to the delay in gaining new spells as well as the fact that you're going to be keeping that spell chucker out of melee anyway, so you don't really need to worry too much about those save boosts and immunity. That's not to say a Pally/SOR wouldn't work, but pure Sorcerer would be better. One of the Paladin 'flavors' allows you to freely multiclass with Fighter, so that could be a decent mix (PAL/FTR).
One level of Rogue and then going specialist WIZ would be a decent idea, depending on the makeup of your party. If you have a SOR or two along with him, then you'd be golden.
Recently I played through IWD2 a couple times and had good fun with the following party:
1/2 Orc Fighter. He specialized in a two-handed weapon - polearm or greatsword (I did a couple runs and used the same type of character, trying one of these weapons in each run). He also specialized in another melee weapon so I could grab Maximized Attack, which can be a fun feat.
Dwarf FTR 1/CLC X. This guy was a cleric of Tempus, which gave him the free Martial Weapon Battle Axe and Weapon Focus Battle Axe feats. The level of FTR just granted him an extra feat, which is useful. I used him as a secondary tank, focusing on buff spells and healing, as opposed to trying to bother with offensive spells. I only pumped Wisdom enough to be able to cast the spells I wanted. Other ability boosts went to STR. On another run I went with a more spell casting focus, but didn't enjoy it as well as the battle oriented character.
Wild Elf Fighter. This one was mainly focused on ranged attacks, specializing in the bow and taking the few ranged-oriented feats available. I also grabbed the dual weapon fighting feats, and specialized him in small swords, using a pair of short swords, daggers or one of each when there was need to melee. On another run I did a 30/30 split of FTR and Rogue with this character and it worked out very well.
Tiefling Rogue 1/WIZ (sometimes I specialize this one). The INT and DEX bonus was the incentive to go with this race for this character. Even though the level progression was slowed due to the late acquisition of WIZ levels, he was still fun and effective. I dropped this character on the run where I went with the FTR/Rogue and slipped another melee character into this slot instead: a PAL/FTR.
Human SOR. Pretty self explanatory here, but this one as the party 'face'. She took all the social skills (Bluff, Intimidate, Diplomacy) as well as Knowledge:Arcana, Alchemy, and Concentration and Spellcraft (I maxed out her INT for the skill points).
Aasimar SOR. Slightly delayed spell progression due to the racial adjustment, but the +1 to CHA is a nice bonus. On another run, just for yucks, I went with a Strongheart Halfling for this character.
Obviously there are stronger/more optimized parties, but I'm an incorrigible min/maxer and these combos were more than powerful enough to wipe the floor with the competition with my min/maxing.