Greetings,
I would use HTML::Template to set up a table for image display, 5 per row, as many rows as needed. Something like

<table border="0" cellpadding="4" cellspacing="1" bgcolor="#000000">
<TMPL_LOOP name="rowloop">
  <tr bgcolor="#ffffff">
    <td valign="top">
      <TMPL_IF name="img1src">
      <img src="/cgi-bin/thumbnail.pl?img=<TMPL_VAR name="img1src">">
      </TMPL_IF>
    </td>
    <td valign="top">
      <TMPL_IF name="img2src">
      <img src="/cgi-bin/thumbnail.pl?img=<TMPL_VAR name="img2src">">
      </TMPL_IF>
    </td>
    <td valign="top">
      <TMPL_IF name="img3src">
      <img src="/cgi-bin/thumbnail.pl?img=<TMPL_VAR name="img3src">">
      </TMPL_IF>
    </td>
    <td valign="top">
      <TMPL_IF name="img4src">
      <img src="/cgi-bin/thumbnail.pl?img=<TMPL_VAR name="img4src">">
      </TMPL_IF>
    </td>
    <td valign="top">
      <TMPL_IF name="img5src">
      <img src="/cgi-bin/thumbnail.pl?img=<TMPL_VAR name="img5src">">
      </TMPL_IF>
    </td>
  </tr>
</TMPL_LOOP>
</table>
[download]

As for resizing you could create a script that reads in a single image and outputs the resized version, like a thumbnail, You will need GD or Image::Magic for this. Then with your gallery script fill the HTML::Template with image tags that call the thumbnail script i.e. <image src="/cgi-bin/thumbnail.pl?img=foobar.jpg" /> That way you don't have to slurp the entire directory of images in, just their names.

Update Fixed Template formatting for readability

-InjunJoel