The ambidexterity skills detailed in Fields Of Fire (p.81) state that 'Any time the character attempts to use his off-hand (non-dominant hand), he must apply a negative modifier to the target number equal to the appropriate Skill Rating, minus the Special Skill. ... An Ambidexterity Skill Rating higher than the rating of the skill being used has no effect.'

If I understand this rule correctly, it means that a character with an ambidexterity skill of 1 is actually better at attacking with his off-hand, than a character with an ambidexterity skill of 3.

I will use the example shown in Fields of Fire to demonstrate.

'... a character with a Firearms Skill of 5 and Ambidexterity of 3 attempting to shoot with her off-hand must apply a -2 (5-3) modifier.'

So if you have a Firearms of 5 and an Ambidexterity Skill of 1, you must apply a -4 (5-1) modifier.

And, if FASA meant that you are supposed to subtract the Firearms Skill from the Special Skill, then people of a higher Skill Rating in Firearms are worse at using their off-hand, than people with low Ratings.

I have created some rules to solve this problem:

If a character is attempting to use a ranged weapon in his non-dominant hand, then apply a Target Modifier of +2 to the attack.
If a character is attempting to use ranged weapons in both hands, apply a Target Modifier of +3 to the non-dominant attack, and +2 to the dominant attack.
If a character is making a melee attack, then increase the target modifiers by 1 (+4 non-dominant, +3 dominant).

Also, if a character is attacking with two weapons, then the skill should be split, and the larger of the two would be used for his dominant attack. Combat pool however, does not necessarily have to be split.

A character attacking more than one opponent with ranged attacks, must apply a +1 Target Modifier to all target numbers .

A character splitting his melee attacks between two opponents must apply a +2 Target Modifier to both attacks.

Subtract the character's Ambidexterity Skill Rating from this modifier to a minimum of +0.
The Ambidexterity Skill has a maximum rating of 3.

Thus, a character with an Ambidexterity Skill of 2, attacking at short range with two Ares Predators and no other modifiers (smartgun, etc), would have a Target Number of 5 (basic target number of 4, +3 off-hand modifier, -2 for ambidexterity) to his off-hand attack, and a Target Number of 4 (basic target number of 4, +2 dominant attack modifier, -2 ambidexterity), to his on-hand attack.

The same character attacking with two knives would have a Target Number of 6 (base 4, +4 non-dominant, -2 ambidexterity) for his non-dominant attack, and a Target of 5 with his dominant attack.