I suggest trying the following:
Please pay attention to the type of parentheses - or braces in your input. Mathematica is very pedantic about it. Although there usually are numerous ways to accomplish a certain goal in Mathematica, input syntax itself doesn't have many synonymous forms.

Second issue that might be relevant here is the fact that FindRoot fails to find real-valued roots for your equation. This is probably because your input parameters are imprecise. Instead of getting bogus results and lots of warnings, I started with complex-valued guess (4 + I), which finds complex-valued roots. Chop removes very small terms from the results - all imaginary parts for the roots are eliminated in this way. I don't know if these results make sense to you; basically root would seem to be more or less precisely zero for every input.

I suggest finding a good tutorial for learning use of Mathematica. It is a bit too large system to learn in a random fashion from the start. Getting a good idea of its' fundamentals takes unfortunately at least couple weeks. I've been personally using it occasional manner - on and off - for almost two decades, and only after couple first years I actually grasped most of the fundamental ideas. Still at this point, I find new stuff at least once a week. It's a powerful system, but like all power tools, tends to demand rigorous approach to learning...

Jari, thanks for helping.  Upon further searching I believe an Array would be able to satisfy what I need.  I'm thinking I could calculate Specific Volume values over an array of  Van der Waal equations for the given Pressure change.  Another thing I need to do is plot the curve for Pressure vs Specific Volumes.  So this method would work well for getting data points.

However, I've been trying and don't understand the Array format.  For version 8, can someone point me in the right direction for this?