Hey terror,
Brio is right. You will need to use a non-breaking space however since there are no letters in front to allow for a normal space. This can be accomplished in Dreamweaver by simply using Ctrl Shift Spacebar or by finding the insert nonbreaking space button within your objects pallete.
Just in case this is unclear, The code should look like this:
<body bgcolor="#FFFFFF" text="#000000">
<table width="520" border="0" cellpadding="0" cellspacing="0" bgcolor="#999999">
<tr>
<td width="520" height="336"> </td>
</tr>
</table>
</body>
Another option would be to place a spacer image (usually a one by one pixel transparent gif) inside your table and change the size within Dreamweaver to match your table (not always necessary, but cleaner: you could leave it one by one pixel in most cases).
This technique is neccesary when using very small table cells within tables. (smaller than the room a nonbreaking space requires)
Let me know if this helps.