[imported_plattopus]

This is a simple HTML edit as you anticipated.

Change this:

$post[avatar]<br><p><b>$post[username]</b></normalfont><br>
	<smallfont>$post[usertitle]</smallfont><br>
	<p></div>
	<smallfont>Registered: $post[joindate]<br>
	Location: $post[field2]<br>
	Posts: $post[posts]</smallfont></td>

To this:

$post[avatar]<br><p><b>$post[username]</b></normalfont><br>
	<table width="98%" cellpadding="3" cellspacing="0">
	<tr>
		<td width="100%" bgcolor="blue">
		<smallfont>Registered: $post[joindate]<br>
		Location: $post[field2]<br>
		Posts: $post[posts]</smallfont>
		</td>
	</tr>
	</table></td>

Change all values in red to whatever you prefer.

Note: this is untested, but should work fine.