Problem with posting messages in php

I’m trying to make a very simple forum and I have a problem with posting the messages. If I press the refresh button after I posted the message the message gets posted again. I’ve already tried to unset the variables but it doesn’t seem to work.
here is the code
<code>
[size=2]<[/size][size=2][color=#000080]html[/color][/size][size=2]>

<[/size][size=2][color=#000080]head[/color][/size][size=2]>

<[/size][size=2][color=#000080]title[/color][/size][size=2]>forum</[/size][size=2][color=#000080]title[/color][/size][size=2]>

</[/size][size=2][color=#000080]head[/color][/size][size=2]>

<[/size][size=2][color=#000080]body[/color][/size][size=2][color=#000080]bgcolor[/color][/size][size=2]=[/size][size=2][color=#008000]#cccccc>

[/color][/size][size=2]<[/size][size=2][color=#000080]table[/color][/size][size=2][color=#000080]align[/color][/size][size=2]=[/size][size=2][color=#000080]center[/color][/size][size=2][color=#000080]width[/color][/size][size=2]=[/size][size=2][color=#ff00ff]“78%” [/color][/size][size=2][color=#000080]border[/color][/size][size=2]=[/size][size=2][color=#ff00ff]“0” [/color][/size][size=2][color=#000080]cellspacing[/color][/size][size=2]=[/size][size=2][color=#ff00ff]“0”[/color][/size][size=2]>

**<?**php

[/size][size=2][color=#0000ff]require_once[/color][/size]size=2;

[/size][size=2][color=#0000ff]if[/color][/size][size=2]([/size][size=2][color=#0000ff]isset[/color][/size]size=2[/size][size=2]&& $HTTP_POST_VARS**[[/size][size=2][color=#ff00ff]‘mesaj’[/color][/size][size=2]]!=[/size][size=2][color=#ff00ff]’’[/color][/size][size=2])**

{$mesaj**=$HTTP_POST_VARS[[/size][size=2][color=#ff00ff]‘mesaj’[/color][/size][size=2]]**;

@ $db**=mysql_connect([/size][size=2][color=#ff00ff]‘localhost’[/color][/size][size=2],[/size][size=2][color=#ff00ff]‘bebe’[/color][/size][size=2],[/size][size=2][color=#ff00ff]‘gaboronerone1’[/color][/size][size=2])**;

[/size][size=2][color=#0000ff]if[/color][/size]size=2{[/size][size=2][color=#0000ff]echo[/color][/size][size=2][color=#ff00ff] ‘Imi pare rau dar conexiunea la baza de date nu s-a putut realiza’[/color][/size][size=2];[/size][size=2][color=#0000ff]exit[/color][/size][size=2];}

[/size][size=2]mysql_select_db**([/size][size=2][color=#ff00ff]‘forum’[/color][/size][size=2])**;

$user**=**[/size][size=2][color=#ff00ff]‘gabor_cata’[/color][/size][size=2];

$[/size][size=2][color=#000080]data[/color][/size][size=2]=getdate([/size][size=2][color=#ff00ff]‘year mon mday’[/color][/size][size=2]);

$query**=**[/size][size=2][color=#ff00ff]“insert into discutii values(’”[/color][/size][size=2].$user.[/size][size=2][color=#ff00ff]"’,’"[/color][/size][size=2].$[/size][size=2][color=#000080]data[/color][/size][size=2].[/size][size=2][color=#ff00ff]"’,’"[/color][/size][size=2].$mesaj.[/size][size=2][color=#ff00ff]"’)"[/color][/size][size=2];

$result**=mysql_query($query)**;

[/size][size=2][color=#0000ff]unset[/color][/size]size=2;

[/size][size=2][color=#0000ff]unset[/color][/size]size=2;

}

@ $db**=mysql_connect([/size][size=2][color=#ff00ff]‘localhost’[/color][/size][size=2],[/size][size=2][color=#ff00ff]‘bebe’[/color][/size][size=2],[/size][size=2][color=#ff00ff]‘gaboronerone1’[/color][/size][size=2])**;

[/size][size=2][color=#0000ff]if[/color][/size]size=2 {[/size][size=2][color=#0000ff]echo[/color][/size][size=2][color=#ff00ff] ‘Imi pare rau dar serverul mysql nu este ****it’[/color][/size][size=2];[/size][size=2][color=#0000ff]exit[/color][/size][size=2];}[/size]
</FONT>[size=2]
[/size][size=2]mysql_select_db**([/size][size=2][color=#ff00ff]‘forum’[/color][/size][size=2])**;

$query**=**[/size][size=2][color=#ff00ff]“select * from discutii”[/color][/size][size=2];

$result**=mysql_query($query)**;

$num_rez**=mysql_num_rows($result)**;

[/size][size=2][color=#000080]for[/color][/size]size=2

{$row**=mysql_fetch_array($result)**;

[/size][size=2]afisare**($row[[/size][size=2][color=#ff00ff]‘user’[/color][/size][size=2]],$row[[/size][size=2][color=#ff00ff]‘mesaje’[/color][/size][size=2]],$row[[/size][size=2][color=#ff00ff]‘data’[/color][/size][size=2]])**;

[/size][size=2][color=#0000ff]echo[/color][/size][size=2][color=#ff00ff] “<br>”[/color][/size][size=2];

}

?>

</[/size][size=2][color=#000080]table[/color][/size][size=2]>

<[/size][size=2][color=#000080]form[/color][/size][size=2][color=#000080]action[/color][/size][size=2]=[/size][size=2][color=#ff00ff]“forum.php” [/color][/size][size=2][color=#000080]method[/color][/size][size=2]=post>

<[/size][size=2][color=#000080]center[/color][/size][size=2]>

<[/size][size=2][color=#000080]textarea[/color][/size][size=2][color=#000080]name[/color][/size][size=2]=[/size][size=2][color=#ff00ff]“mesaj”[/color][/size][size=2]:[/size][size=2][color=#000080]cols[/color][/size][size=2]=[/size][size=2][color=#ff00ff]50 [/color][/size][size=2][color=#000080]rows[/color][/size][size=2]=[/size][size=2][color=#ff00ff]6 [/color][/size][size=2]wrap**=hard [/size][size=2][color=#000080]value[/color][/size][size=2]=[/size][size=2][color=#ff00ff]’’[/color][/size][size=2]></[/size][size=2][color=#000080]textarea[/color][/size][size=2]>**

<[/size][size=2][color=#000080]BR[/color][/size][size=2]>

<[/size][size=2][color=#000080]input[/color][/size][size=2][color=#000080]type[/color][/size][size=2]=submit[/size][size=2][color=#000080]value[/color][/size][size=2]=posteaza>

<[/size][size=2][color=#000080]center[/color][/size][size=2]>

</[/size][size=2][color=#000080]form[/color][/size][size=2]>

</[/size][size=2][color=#000080]body[/color][/size][size=2]>

</[/size][size=2][color=#000080]html[/color][/size][size=2]>

[/size]</code>