A question about Doom

If any1 here owns Doom 3 or has knowledge of it please answer this topic.

1. How is the Doom 3 coop and can u do splitscreen or on live?

2. What is Doom 3: Ressurection of Evil and does this have coop online or splitscreen?

3. What is the Doom 3 Collectors Edition and is it still sold?

4. Should i just buy Quake 4???

Thanx to whoever answers...