Im not exactly sure if this is what you meant but you could try one of these.
<table background="some.img">
<tr><td colspan=3> </td></tr>
<tr>
<td width=10> </td>
<td bgcolor="white">your text here</td>
<td width=10> </td>
</tr>
<tr><td colspan=3> </td></tr>
</table>
or...
<table background="some.img" cellpadding=10 height=500 width=500>
<tr><td>
<table bgcolor=white height=400 width=400>
<tr><td>your text</td></tr>
</table>
</td></tr>
</table>
those are rough hacks, you would have to play with it to acheive what you like. you could also try finding a site that does what you're looking for and then copying their HTML.