[Simon Lloyd]

You can find it in this template: modifyprofile and use a condtional for your condtion to hide this

<fieldset class="fieldset">
				<legend><label for="tb_homepage">$vbphrase[home_page_url]</label></legend>
				<table cellpadding="0" cellspacing="$stylevar[formspacer]" border="0" width="100%">
				<tr>
					<td>$vbphrase[let_other_visitors_know_url]</td>
				</tr>
				<tr>
					<td>$vbphrase[home_page_url]<br /><input type="text" class="bginput" name="homepage" id="tb_homepage" value="$bbuserinfo[homepage]" size="50" maxlength="200" dir="ltr" /></td>
				</tr>
				</table>
			</fieldset>

like this

<if condition="!is_member_of($bbuserinfo, X, Y, Z)">
<fieldset class="fieldset">
				<legend><label for="tb_homepage">$vbphrase[home_page_url]</label></legend>
				<table cellpadding="0" cellspacing="$stylevar[formspacer]" border="0" width="100%">
				<tr>
					<td>$vbphrase[let_other_visitors_know_url]</td>
				</tr>
				<tr>
					<td>$vbphrase[home_page_url]<br /><input type="text" class="bginput" name="homepage" id="tb_homepage" value="$bbuserinfo[homepage]" size="50" maxlength="200" dir="ltr" /></td>
				</tr>
				</table>
			</fieldset>
</if>

Which says if the users are NOT in usergroup X, Y or Z then they cannot see this info.