The following is a conversion between the d20 World of Darkness (WoD) system character types "Werewolf" and "Vampire" to d20 Modern rules.
In d20 WoD, all characters start with 4 hit dice, 16 times their skill points per level, and one ability score point to spend freely. A "1st level" WoD character is considered to be CR 4. All together, this strongly implies that WoD characters are effectively 4th level in d20 modern terms when they start out.
If you want to take a WoD character type in place of a d20 Modern class, you'll need to have some levels which lead up to that 1st level - otherwise you'll be getting 4 levels for the price of 1.
Here's my plan to do that. Please take a look and see if you can spot any problems.
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WoD Werewolf for d20 Modern
The prospective Werewolf character begins their transformation without the ability to shapechange. Rites selected before 4th level ("Level 1" by the WoD book, pg 75) cannot rely on shapechanging.

• Hit points: 1d12 + CON bonus
• Skill points: 2 + INT bonus
• Action points: 5 + (level / 2)
• Wealth Bonus: as d20 Modern
• Class skills: choose 2 themes from pg81 WoD

Level -2 Werewolf

• BAB +1
• Defence +0
• Fortitude +2, Reflex +0, Will +0
• Features: Essence, Rite
• Reputation +0
• Ability scores: +2 to STR or CON

Level -1 Werewolf

• BAB +2
• Defence +1
• Fortitude +2, Reflex +1, Will +0
• Features: Hardiness, Sprint Healing
• Reputation +0

Level 0 Werewolf

BAB +1
• Defence +1
• Fortitude +3, Reflex +1, Will +1
• Ability scores: +2 to STR or CON

After that, your next level will be Level 1 of Werewolf, and except where noted below, it'll be as written in the WoD book:

• BAB +1 (and +1 per level hereafter)
• Hit Points: 1d12 + CON adjustment
• Shapechanging: as WoD pg 75
• Auspice Ability
• Werewolf weaknesses
• Regaining Essence: you will not gain essence from eating freshly killed humans' hearts - instead, you gain one point of essence if you hunt down and eat any animal using only your natural weapons (claws, bite). The creature must be hunted - you cannot pounce on a friendly domestic dog or cat, it has to have fled in fear first.

WoD Vampire for d20 Modern
As the prospective vampire character descends into damnation, his powers increase, but he retreats into darkness, eventually being cursed to burn in daylight. Until the vampire has fully turned, he gains no Vitae from drinking blood, and so cannot use Disciplines that require it.

• Hit points: 1d8 + CON bonus
• Skill points: 4 + INT bonus
• Action points: 5 + (level / 2)
• Wealth Bonus: as d20 Modern
• Class skills: choose 2 themes from pg81 WoD

Level -2 Vampire

• BAB +1
• Defence +1
• Fortitude +2, Reflex +2, Will +2
• Features: Predator's Taint, Discipline, Light Sensitive (dazzled, plus additional -2 to all checks in daylight or similarly bright light)
• Reputation +1
• Ability scores: +2 to CHA, +2 STR or CON

Level -1 Vampire

• BAB +1
• Defence +1
• Fortitude +3, Reflex +3, Will +3
• Features: Bite, Resistance to Damage (critical multiplier -1), Blood addiction
• Reputation +1
• Ability scores: +2 STR or CON

Level 0 Vampire

• BAB +2
• Defence +2
• Fortitude +3, Reflex +3, Will +3
• Features:
  Low Light vision, Discipline, Light Sensitive (as level -2, plus each round in direct sunlight, must make a Fortitude save DC 10 +1 per previous save, or take 1d4 CON damage)
• Reputation +1

On taking level 1 in Vampire, the character gains the abilities and weaknesses listed in WoD pg 69 onwards. He is no longer penalised by bright light, but cannot resist burning in daylight.

Notes
Characters taking WoD Character Types may take other classes in between levels, but none can be WoD Character Types. There are no Werewolf-Vampires by these rules: use the d20 Modern or D&D templates to achieve such aberations.

Critical hits in WoD deal CON damage. Some creatures take Criticals differently. Where a creature has partial immunity to criticals (such as vampires), the critical multiplier of a weapon is reduced by 1.

how do feats work may I ask ?

As normal. You get one every three level, except when you get a bonus feat, which is noted in the class text.

for the vampire I notice that you get certain stat increases, are these in addition to the ones you get for being a vampire?

No, those are the ones you get for being a vamp.
You'll get more again at 1st level from whichever clan you select at that time.

Mage, d20 conversion

Hit Die: d6
Skill Points: 4 + INT modifier
Choose two skill groups from MCWoD pg 81 as class skills
Spells: Spellcraft is a class skill. You may use component points to cast spells.

Level -2
Base Attack Bonus +0
Fort +0, Ref +0, Will +2
Defence +0
Components: 15
Gnosis
Improvised Magic: you can invent spells using components.

Level -1
Base Attack Bonus +1
Fort +0, Ref +0, Will +3
Defence +0
Components: 30
Mental ability adjustment +2
Secrets of the Path: Choose one path (pg 194 MCWoD): this is your Mage Path. You know these rote spells. You do not gain the +5 bonus on spellcraft.

Level 0
Base Attack Bonus +1
Fort +1, Ref +1, Will +3
Defence +1
Components: 45
Gnosis
Stolen Secrets: Choose another path - you know the rote spells of that path.
Skills of the Path: gain a +5 Spellcraft check on rote spells of your path.

Level 1
Base Attack Bonus +2
Fort +1, Ref +1, Will +4
Defense +1
Components: 60
Rote Mastery: you know all rotes, and gain a +5 bonus to spellcraft checks to cast them. This bonus stacks with the +5 from Skills of the Path.