Hi, here's Karsten Heymann's solution sent by TEX-D-L. Strictly speaking, there are 2 ways to solve the problem. Thanks a lot, Karsten!
Regards Detlev \begin{table} \tiny \caption{Karsten's Solution} \begin{tabular}{cccc} \multirow{2}{10mm}{$\smash{\left.\rule{0pt}{4mm}\right\}}{}\smash{^e}000,0$} & \multirow{2}{10mm}{$\smash{^g}000,0$} & \multirow{2}{10mm}{$\smash{^j}000,0$} & \multirow{2}{10mm}{$\smash{^z}000,0$} \tabularnewline & & & \tabularnewline \end{tabular} \bigskip \begin{tabular}{cccc} \multirow{2}{10mm}{$\smash{\left.\rule{0pt}{4mm}\right\}}{}^{\mathstrut e}000,0$} & \multirow{2}{10mm}{$^{\mathstrut g}000,0$} & \multirow{2}{10mm}{$^{\mathstrut j}000,0$} & \multirow{2}{10mm}{$^{\mathstrut z}000,0$} \tabularnewline & & & \tabularnewline \end{tabular} \end{table} In LyX you only have to modify the multirow-ERT-boxes. \smash{} rejects height (and depth) of the content in braces. \mathstrut puts in an invisible "prop" with the height of the current font size. If necessary \raisebox{height}{text} for vertical fine tuning.