I have downloaded pgf from
http://www.ctan.org/tex-archive/help/Catalogue/entries/pgf.html

and unzip base.zip
under
minimals-beta/tex/texmf-context/tex/context/pgf
then
$> context test-alan
It seems to work

minimals-beta
Linux luigicasa-laptop 2.6.24-21-generic #1 SMP Mon Aug 25 17:32:09 UTC 2008 i686 GNU/Linux
This is LuaTeX, Version snapshot-0.30.2-2008102016, build unknown
ConTeXt MtxRun | current version: 2008.10.23 17:32




%% test-alan.tex %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usemodule[tikz]
\setupcolors[state=start]
\starttext
Hello, world!
\blank
\begingroup
\tikz \draw[thick,rounded corners=8pt]
  (0,0) -- (0,2) -- (1,3.25) -- (2,2) -- (2,0) -- (0,2) -- (2,2) -- (0,0) -- (2,0);
\endgroup

\starttikzpicture
  \draw[fill=yellow] (0,0) -- (60:.75cm) arc (60:180:.75cm);
  \draw(120:0.4cm) node {$\alpha$};
  \draw[fill=green!30] (0,0) -- (right:.75cm) arc (0:60:.75cm);
  \draw(30:0.5cm) node {$\beta$};
  \startscope[shift={(60:2cm)}]
    \draw[fill=green!30] (0,0) -- (180:.75cm) arc (180:240:.75cm);
    \draw (30:-0.5cm) node {$\gamma$};
    \draw[fill=yellow] (0,0) -- (240:.75cm) arc (240:360:.75cm);
    \draw (-60:0.4cm) node {$\delta$};
  \stopscope
  \startscope[thick]
    \draw (60:-1cm) node[fill=white] {$E$} -- (60:3cm) node[fill=white] {$F$};
    \draw[red]                   (-2,0) node[left] {$A$} -- (3,0) node[right]{$B$};
    \draw[blue,shift={(60:2cm)}] (-3,0) node[left] {$C$} -- (2,0) node[right]{$D$};
    \draw[shift={(60:1cm)},xshift=4cm]
    node [right,text width=6cm,rounded corners,fill=red!20,inner sep=1ex]
    {
      When we assume that $\color[red]{AB}$ and $\color[blue]{CD}$ are
      parallel, i.\,e., ${\color[red]{AB}} {|} \color[blue]{CD}$,
      then $\alpha = \delta$ and $\beta = \gamma$.
    };
  \stopscope
\stoptikzpicture
\stoptext