If you add padding:10px to your CSS, you can give the elements enough space around them so that they aren't right up against the borders:
#replies td{
border-collapse:collapse;
border:1px solid black;
padding:10px;
}
Here is your updated jsfiddle to give you an idea of what that would look like.
Next, to fix the problem with the radio buttons, put a <span> around both Single and Multiple, and get rid of the space. Also, add a div around each input/span pair. Afterwards, add this to your CSS:
span {
padding-left:5px;
}
See this jsfiddle for an example.
Here is the modified HTML:
<tr>
<td>Number of <br/>Replies: </td>
<td align="left">
<div class="td">
<input type="radio" name="reply" value="single" class="replyBtn" />
<span>Single</span>
</div>
<div class="td">
<input type="radio" name="reply" value="multiple" class="replyBtn" />
<span>Multiple</span>
</div>
</td>
</tr>