[texhax] how to overwrite the default figure number

[Tao Shi]

For example, I use the following code to include a figure in my text and 
this is the 2nd figure in the text.

...

\begin{figure}[htp]
    \centerline {\includegraphics [width=14cm, viewport=60 315 545 573, 
clip] {fig2}}
    \centering
    \caption[]{}
    \label{fig2}
\end{figure}

....

By default, LaTex will put "Figure 2:" under the figure.  What if I want to 
change it to something like "Figure A.2:", how can I do it?

Thanks,

...Tao