
The following represents the IMHO of Gruntboy and is not meant to be an exhaustive guide to dual classing.

The rules
Humans only can dual class.
Dual classes must also be viable multiclass characters (its to do with the display buttons). Bards, Monks etc. cannot dualclass.
You must have stats of 15+ in your prime requisites for your first class and 17+ in the prime requisites of the class you are dualling to. (e.g. fighter dualled to mage must have str 15, int 17).
You can pick a kit for the first class but not for the one you are dualling to.
You can only dual class once (i.e. no fighter/mage/thief "triple class").
You must abide by class restrictions (e.g. kensai/mage can't wear armour, figher/thief can wear chainmail but can't backstab wearing it).
Your first class is re-activated after obtaining one level higher in the second class (level 9 berserker>level 10 cleric for example.
There's more - fill in the blanks guys & gals.
The options
(note: style in the following is: first class>second class)
Don't dual from a first class cleric - the kits aren't great and you will limit your cleric spell progression.
Don't dual from a first class mage - you will limit your mage spell progression. *Exception* - mage level 2>Fighter or thief allows that character to use spell scrolls, wands and mage-only items (staff of magi). You only have to use 1d4 for hitpoints for 2 levels and you will have lots of brains to be sucked by Illithids

Dualling from a first class thief kit can let you have a great fighter, mage or cleric with thief skills but you will be forgoing the benefits a high level thief obtains. On the other hand you can maximise thief skill in areas that count quickly and then dual to progress fully in the second class. Because thieves level up quickly you can dual faster but it will therefore take you longer to re-activate your thief skills as every other class levels up more slowly.
Dualling from a fighter kit is popular - you can earn excellent weapon proficiencies and get the benefit of 9d10 + full constitution bonus before moving to +3 HP per level. You can then develop fully as a mage or cleric.
Dualling from whatever into a thief is not a great choice. You can't pick a thief kit (a X class>assassin or bounty hunter would've been great) and you will maximise your thief skills quickly. However, you will be able to dual later in the game (achieve a higher first class) and re-activate more quickly.
Next... specifics

[This message has been edited by Gruntboy (edited 04-05-2001).]