[RS_Jelle]

The reason is simple: you are using some wrong code.

I find in the HTML source code of your HPIA Ligt style the following piece (header template):

<table border="0" width="100%" cellpadding="0" cellspacing="0" align="center">
<tr>
	<td align="left"><a href="index.php"><img src="http://i73.photobucket.com/albums/i206/62442al_Man/ikkeheltgladidennesl2.jpg" border="0" alt="HP In Action" /></a></td>
	<td align="right">

		&nbsp;
	</td>
</tr>
</table>

The table is a 100% stretch one and the first cell (td) is aligned at the left and the logo is stated in that one ...

Change it to for example:

<table border="0" width="100%" cellpadding="0" cellspacing="0" align="center">
<tr>
	<td align="center"><a href="index.php"><img src="http://i73.photobucket.com/albums/i206/62442al_Man/ikkeheltgladidennesl2.jpg" border="0" alt="HP In Action" /></a></td>
</tr>
</table>

So without a right cell (it's useless because it's empty) and the left cell centered.

This should do the trick