[Tim Wheatley]

Infact here you go. PLEASE BACKUP because I really don't consider myself a hacker and I don't want you to mess your board up:

In template... User Option Templates > modifyoptions >

Remove:

<tr>
	<td bgcolor="{secondaltcolor}"><normalfont><b>Default Posts per Thread:</b></normalfont><br>
	<smallfont>Number of posts that are shown on one page of a thread.</smallfont></td>
	<td bgcolor="{secondaltcolor}"><smallfont>
	<select name="umaxposts">
		<option value="-1" $postsdefaultselected>Use forum default</option>
		$maxpostsoptions
	</select></smallfont></td>
</tr>

That will stop the users from changing your posts per page setting.

Then go to the VB Admin panel > VBulletin Options > Thread display options >

In the 'User Settable Maximum Posts per Page' box, only put in the number you want to be available. eg: '40' = 40 posts per page.

Next enter the following sql query into your database:

UPDATE user SET maxposts=40;

I *think* that's right, but obviously change 40 to what you want per page.