[pstricks] pstricks plot in a floating figure is drawn above text

[George]

I tried to include a plot in my document using:

%~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
\begin {figure}[ht]
\begin {center}
%\includegraphics[width=\figurewidth]{dram_price.eps}
\psset{xunit=.5cm,yunit=4.5cm}
 \savedata{\mydata}[
 {{0, 0}, {1., 0.946083}, {2., 1.60541}, {3., 1.84865}, {4.,
.7582},
 {5., 1.54993}, {6., 1.42469}, {7., 1.4546}, {8., 1.57419},
 {9., 1.66504}, {10., 1.65835}, {11., 1.57831}, {12., 1.50497},
 {13., 1.49936}, {14., 1.55621}, {15., 1.61819}, {16., 1.6313},
 {17., 1.59014}, {18., 1.53661}, {19., 1.51863}, {20., 1.54824}}]
 \dataplot[plotstyle=curve,showpoints=true,
 dotstyle=triangle]{\mydata}
 \psline{<->}(0,2)(0,0)(20,0)
\end {center}
\caption {Prices of different capacity DRAM chips in 1977 dollars
			\cite{patt_and_henn_quantitative}}
\label {dram_price}
\end {figure}
%~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

But what I get is this:

http://i31.tinypic.com/5dm5io.png

Isn't it possible to have pstricks as a floating figure?