1. Feats: I would explain a feat as something like a skill that a character has particularly worked on or a natural talent. For example, I would liken some skills to a character having decided to specialize in a weapon or a skill. This uses something that a 2nd Edition player knows about (weapon specialization) to help explain a new concept. Analogies probably will prove helpful, Spider.
2. The higher the better: This applies to AC, Base Attack Bonus, and skill rolls. Generally, explain that to hit an armor class or succeed at a skill, you have to either equal or beat the AC or the difficulty class.
3. Races: No more level limits, which is something I suspect a lot of 2nd Edition groups ignored. I could never see the justification for them. Similarly, it is possible to play against 2nd edition archetypes. A dwarven wizard in a 3.5 game can be a formidable character. (The constitution bonus helps with hit points.)
4. Saving Throws: Simplified to three categories: Fortitude: Anything that you have to make your body resist, such as poison or energy drain. Reflex save: Anything you can jump away from, such as a fireball. Will save: You have enough willpower to say no to the Count Dracula wannabe.
5. Classes: The classes are designed to be more closely balanced with each other. Thus a 1st level caster is generally good for more than just one spell. Skills also tend to make a character more viable, level per level, than in 2nd Edition.
6. Categories of effects: Certain types of effects, such as energy drain and the like, work similarly between different creatures.
7. Damage Resistance: Certain materials overcome damage resistance of a given creature better than others. Even if you don't have a silver weapon, you might still be able to beat a werewolf. (Under 1st and 2nd Edition rules, a character without a silver or magic weapon could not damage a lycanthrope.)
8. Armor: Bulkier armors, such as plate, tend to limit how much dexterity you can put into your armor class. Similarly, there are different types of AC modifiers, such as armor, deflection, and natural armor.
9. Bonus types: Bonuses of different types stack. Bonuses of the same type, such as an enhancement to strength from a magic item and an enhancement to strength from a spell, do not stack.
10. Some things are still the same: Try to point out similarities in concept between different ideas. Demons and devils are 2nd edition creatures, and a demon may be a baatezu. Paladins are still heroic, but their abilities are different from their 2nd Edition counterparts. Again, using analogies between editions help.
11. Prestige classes: Explain this as something like a subclass that someone choses to specialize in. For example, a player may chose to have a character focus on some skills at the expense of other skills.
Spider, good luck with the new players! I hope this helps.