custom webcontrol with placeholder

[gabru]

i am quite new to programming with asp.net and my problem is the following. I want to create a control (or custom-control, etc. sorry i dont know what will be the correct name) which allows me to add a content by myself and take some properties as well ... to be specific i want to create a groupingbox which makes a rounded border over some content .. further i want to specify the width of the control ...

 

here is some pseudocode:

i want to write something like this:

 

<my:Box width="400">
     <content>
            <strong>thats me</strong>
     </content>
</my:Box>

 

and i want the control to do the following when rendered:

 

<table width=400 border=1>
<tr>
    <td><strong>thats me</strong></td>
</tr>
</table>

 

this table is simple but in my specific problem i make a box with rounded corners and i want to reuse this thing in my application. i would be happy to get some example code, examples or just words that i can search for it on the web. Thanks a lot!!