Table will not center (and it is spilling off the right side of the page)

Well your table is too large, so it will either stick out on the right, on the left or on both sides. You can move it to the left with \hspace*{-1cm}\begin{tabular}..., you can center it with e.g. \makebox[0pt]{tabular}

For my PhD-Thesis i've used the trick explained by Stefan Kottwitz. Here's the copied example from his website:

\documentclass[a4paper,10pt]{article}
\usepackage[english]{babel}
\usepackage{blindtext}
\usepackage{tabularx}
\begin{document}

\blindtext

\bigskip

\noindent\makebox[\textwidth]{%
  \begin{tabularx}{1.5\textwidth}{XX}
    \blindtext & \blindtext
  \end{tabularx}
}

\bigskip

\blindtext

\end{document}

The relevant thing is to include your large-ish float into

\noindent\makebox[\textwidth]{%
   %Table or figure
}

Oh, and BTW: I also suggest you look at the booktabs package, it's great for enhancing the display of your tables...

It might be more aesthetically pleasing and easier to maintain if you inserted some line breaks (\\) into your row and column headers that would reduce the overall width of the table. Trying to manually position the table with hspace or similar could wind up looking bad if your page formatting changes in the future.