3e stat conflicts with 4e?

[onetrikpony]

I'm not familiar with any of the older material and I'm wondering;

What are the major conflicts between the old books and 4th edition?

If I used the old Vehicles, Mecha or Robots books to build some gear would it be playable in 4th edition?

The only thing I can see via a quick browse is PD doesn't exist anymore and some of the weapon stats seem a little weird.

Cyberworld and Cthulhu Punk look cool too, are they usable?

I have a chance to swipe a bunch of old dead tree books for free but I don't want to take them if they're just going to waste time and shelf space.