Allot of times you need to have a 1x1 pixel line along the Height of your table. Since you can't set a dynamic height (100%) to a pixel and in any case it's best to use HTML than call an image from the server, you can simply use the background of the <TD>.
The problem is that you usually don't get a width of 1px to your <TD>. The trick here is to set your font size to 1px and make sure table padding is set to 0.
<TABLE CELLPADDING="0">
<TR>
<TD STYLE="background-color:#000000;width:1px;font-size:1px;"></TD>
<TD>
This is a test<BR>
This is a test<BR>
This is a test<BR>
This is a test<BR>
This is a test<BR>
</TD>
<TD STYLE="background-color:#000000;width:1px;font-size:1px;"></TD></TR>
</TABLE>
