Consider the following table. First I have troubles to get the multicolumn-elements in the first row of the table limited to a maximum width (I tried it here with the command C{0.75} but obviously it does not work). The second issue: I would like to have the column-pair "orig." and "norm." centered to each of its multicolumn-elements.
\documentclass{article}
\usepackage{multirow}
\usepackage[ngerman]{babel}
\usepackage{booktabs}
\usepackage{colortbl}
\definecolor{LightGray}{gray}{.8}
\begin{document}
\newcolumntype{C}[1]{>{\centering\arraybackslash}m{#1}}
\begin{table}[htbp]
\centering
\begin{tabular}{C{1.7cm}C{0.75cm}C{0.75cm}C{0.75cm}C{0.75cm}C{0.75cm}C{0.75cm}C{0.75cm}}
\toprule
&
\multicolumn{2}{c}{This is a long text for two rows} &
\multicolumn{2}{c}{This is a long text for three rows} &
\multicolumn{2}{c}{This is a long Text} \\
\multirow{-2}{*}{Row 1} &
org. & norm. &
org. & norm. &
org. & norm. &
\multirow{-2}{*}{Result}\\
\midrule
1 & 0 & 0 & 1 & 0.14 & 7360 & 1 & 0.58 \\
2 & 0.42 & 0.97 & 7 & 1 & 3420 & 0.46 & 0.85 \\
3 & 0.42 & 0.97 & 7 & 1 & 3420 & 0.46 & 0.85 \\
4 & 0.42 & 0.98 & 6 & 0.86 & 3610 & 0.49 & 0.80 \\
5 & 0.43 & 0.99 & 6 & 0.86 & 4100 & 0.56 & 0.82 \\
6 & 0.36 & 0.83 & 5 & 0.71 & 4280 & 0.58 & 0.71 \\
7 & 0.36 & 0.83 & 5 & 0.71 & 4520 & 0.61 & 0.73 \\
8 & 0.43 & 1 & 6 & 0.86 & 4000 & 0.54 & 0.82 \\
9 & 0.27 & 0.63 & 3 & 0.43 & 3920 & 0.53 & 0.54 \\
10 & 0.32 & 0.74 & 5 & 0.71 & 100 & 0.01 & 0.59 \\
\bottomrule
\end{tabular}
\caption{caption}
\label{tab:Example}
\end{table}
\end{document}

multicolumnentries today, you might want to adapt my solution solution given there (or maybe David's ;)). If the multicols still are too wide, try splitting them up into two rows. Moreover, you could make use ofbooktab's\cmidrulecommand to place spanner rules below the multicol headers (cf.booktabsmanual or use search function). Last, the linked answer also shows number alignment withsiunitx, which possibly is of interest, too. – dgs Jun 11 '12 at 19:34tabu-package (http://tex.stackexchange.com/questions/59509/troubles-in-installing-package#59509). – John Jun 11 '12 at 21:50tabularxinstead oftabu. Replace\begin{tabu} spread 1emby\begin{tabularx}{.7\textwidth}, accordingly change the\end{...}group too, and loadtabularxinstead oftabu. – dgs Jun 11 '12 at 22:12