Transparancy Help Options

[liever]

I have a school web page assignment and I'm trying to see if a semi-transparent background behind my text would look better but I cant seem to get it exactly right.

Example

Alright see my problem?
Whenever I try and add in a transparancy code, it turns the whole DIV transparent, which I dont want. I just want the black background of the DIV, which is behind the text, semi transparent. If that makes sence.

The code I've got going on is something like this, for the DIV segment I want transparent:

CODE

#onediv{
[b]{filter: alpha(opacity=55); -moz-opacity: .55; background-color:#000000;[/b]
left:400px;
width:474px;
position:absolute;
top:400px;
}

I've tried many different ways and I'm not able to get the exact thing I want.
it always turns the WHOLE div to transparent. Which I suppose is what a filter does.
but I can never get JUST the background behind the text to go black.

Its rather agrivating and I think I'm about done with it, which is why I'm asking you lovely kids.

Anyone have any idea?