Don't think the table tool is turned on by default Paul.
To turn it on, you can edit:
ACP -> SYSTEM CORE -> TEMPLATES -> form_editor.tpl -> MODIFY
find this part down the bottom:
image_advtab: true,
plugins: "contextmenu,pagebreak,{if $jrsmiley}jrsmiley,{/if}{if $jrembed}jrembed,media{/if},image,autoresize,{if $table}table,{/if}link,code,fullscreen,textcolor,colorpicker,preview",
toolbar1: "formatselect | fontselect forecolor {if $strong} bold{/if}{if $em} italic{/if}{if $span} underline{/if} | {if $span || $div} alignleft{/if}{if $span || $div} aligncenter{/if}{if $span || $div} alignright{/if}{if $span || $div} alignjustify |{/if}{if $ul && $li} bullist numlist |{/if}{if $div} outdent indent |{/if} undo redo | link unlink anchor pagebreak{if $table} table{/if} | {if $hr} hr{/if}{if $sub && $sup} | sub sup {/if} | code preview fullscreen{if $jrembed || $jrsmiley} |{/if}{if $jrembed} jrembed{/if}{if $jrsmiley} jrsmiley{/if}",
contextmenu: "link image | cut copy paste"
});
add the table plugin if its not already there:
plugins: "contextmenu,pagebreak,
to
plugins: "table,contextmenu,pagebreak,
and the same for the toolbar line, so it should look like this when your finished:
plugins: "table,contextmenu,pagebreak,{if $jrsmiley}jrsmiley,{/if}{if $jrembed}jrembed,media{/if},image,autoresize,{if $table}table,{/if}link,code,fullscreen,textcolor,colorpicker,preview",
toolbar1: "table formatselect | fontselect forecolor {if $strong} bold{/if}{if $em} italic{/if}{if $span} underline{/if} | {if $span || $div} alignleft{/if}{if $span || $div} aligncenter{/if}{if $span || $div} alignright{/if}{if $span || $div} alignjustify |{/if}{if $ul && $li} bullist numlist |{/if}{if $div} outdent indent |{/if} undo redo | link unlink anchor pagebreak{if $table} table{/if} | {if $hr} hr{/if}{if $sub && $sup} | sub sup {/if} | code preview fullscreen{if $jrembed || $jrsmiley} |{/if}{if $jrembed} jrembed{/if}{if $jrsmiley} jrsmiley{/if}",
contextmenu: "link image | cut copy paste"
});
save that and activate the over-ride and reset the caches and you will have the button.
Your users will only be able to use the button if you have allowed
table,tr,td in their quota.
--edit--
Bit hard to see in the code, here's a screenshot of the template editor.
updated by @michael: 04/25/15 12:43:31AM