I've done some research on this topic myself, but I am not a lawyer. If you are seriously considering a competing product to WOD then I recommend talking to a lawyer. But here's my understanding of the law.
Copyright does not cover "ideas". The concept of success/failure on dice rolls is an idea. The part that is actually copyrighted is the writing. Thus you cannot plagiarizer from WOD and the wording of your idea must be your own.
With the disk pool concept, once again it is not infringing on copyright.
However, there is a point where you could be infringing on trademarks. You are creating an RPG, and so does WOD. Your system is SIMILAR to WOD. The real question becomes HOW SIMILAR is it? You need significant differences between your system and theirs to avoid crossing the line to "infringement". If your game is about vampires, werewolves, ghosts, and sorcerers, and you have a similar system, they might have a case. But if you are doing a space adventure system with a similar system, you might be safe.
RPGs when you break them down are essentially collections of stats. How you use those stats are important. You want to make sure that you use different attributes or skills, a different damage system, or change the die mechanics a bit. Maybe instead of 1-10 you do 0-9. Or you have an attribute that modifies the roll but it is the skill/power that determines how many dice you get.
I would aim for at least three MAJOR differences between how your system works and the big name-brand systems.
If you check out my system (link below) you will find several similarities between it and d20, Gurps, and Shadowrun. However, there are several significant differences from each as well. My attributes are roughly 1/2 of a d20 character's score and they are similar in definition. I use d6's similar to Gurps and Shadowrun, but I use a variable number of dice based on how much time devoted to an action. More time = more dice. I track wounds similar to d20, but there is a Stun Roll that determines if my character is affected by the damage. While this is similar to Shadowrun's damage roll-off mechanic, I do it differently. Where d20 hitpoints count down, I have no limit on the number of damage points the character can take.
Then there's the setting, another point of difference.
If you're interested in checking it out, here's the docs: http://www.scribd.com/my_document_collections/2423015