Newbie table formatting/numbering question

I'm trying to format a table like the following:

0.0a summarry       b other summarry
(long)
.1a junk           b more junk
1.0a etc            b so forth


Ie, with all the contents top- and left-aligned and everything lined up semi-nicely and the main columns the same size.

So far the best I've been able to come up with is:

\documentclass{minimal}
\usepackage{amsmath}
\usepackage{fontspec}
\usepackage{array}
\setmainfont{DejaVu Sans}
\title{---}
\date{}
\newcolumntype{T}{>{\vtop\bgroup\vspace*{-\ht\strutbox}\hbox\bgroup}
c<{\egroup\egroup}}
\begin{document}
\begin{tabular}{ T T T l T l }
\hline
0&.0&a&
summary
&b&
other summary (long)
\\ \hline
&.1&a&
junk
&b&
more junk
\\ \hline
1&.0&a&
etc
&b&
so forth
\\ \hline
\end{tabular}
\end{document}

-

\documentclass{article}
\usepackage{amsmath}
\usepackage{fontspec}
\usepackage{array,ragged2e}
\setmainfont{DejaVu Sans}
\begin{document}
\begin{tabular}{ r @{} l >{\RaggedRight}p{3cm} r >{\RaggedRight}p{3cm} } \hline
0.0 &a&  summary &b& other summary (long)        \\ \hline
.1 &a& junk     &b&  more junk \\ \hline
1.0 &a& etc      &b&  so forth  \\ \hline
\end{tabular}
\end{document}


-
\documentclass{article}
\usepackage{booktabs} % <--- for drawing rules
%--------------------------------------
\begin{document}
\begin{tabular}{p{.05\textwidth}p{.4\textwidth}p{.03\textwidth}p{.4\textwidth}}
\toprule
0.0a & summary   &b & other summary (long) \\ \midrule
0.1a & junk      &b & more junk            \\ \midrule
1.0a & etc       &b & so forth             \\ \bottomrule
\end{tabular}
%--------------------------------------
\end{document}


-

It isn't clear what output you are trying to make with the \vtop construction (which isn't really LaTeX at all). It makes each entry a single line with odd vertical alignment. Your suggested output appeared to show 4 columns but the code has 6? If it alternates between a numeric column and a longer description, perhaps tabularx and lXlX is what you are looking for

\documentclass{article}
\usepackage{amsmath}
%\usepackage{fontspec}
\usepackage{array,tabularx,dcolumn}
%\setmainfont{DejaVu Sans}
\title{---}
\date{}

\begin{document}
\centering
\begin{tabularx}\linewidth{D{.}{.}{-1}llXlX}
\hline
0.0&a&  summary    &b&  other summary (long)
\\ \hline
.1&a& junk &b&  more junk
\\ \hline
1.0&a& etc    &b&    so forth
\\ \hline
\end{tabularx}
\end{document}

-
The code has 6 columns to get the components of each number to line up (eg, the .1 directly below the .0). –  David X Mar 26 '12 at 12:02
oh in that case you could use dcolumn I have updated my answer –  David Carlisle Mar 26 '12 at 12:58