[HTML][CSS]Problem z Float Opcje

[Raven1122]

Witam mam taki styl css:

[HTML] pobierz, plaintext 
#leftmenu{
background:#f5f5f5;
background-image:url("../images/div_top.png"),url("../images/div_bottom.png");
background-position:top center, bottom center;
background-repeat:repeat-x, repeat-x;
width:290px;
height:100%;
border:1px solid #b7b7b7;
float:left;
}
 
#centerblock{
background:#f5f5f5;
background-image:url("../images/div_top.png"),url("../images/div_bottom.png");
background-position:top center, bottom center;
background-repeat:repeat-x, repeat-x;
width:500px;
height:100%;
border:1px solid #b7b7b7;
margin-left:295px;
}
 
#rightmenu{
background:#f5f5f5;
background-image:url("../images/div_top.png"),url("../images/div_bottom.png");
background-position:top center, bottom center;
background-repeat:repeat-x, repeat-x;
width:170px;
height:100%;
border:1px solid #b7b7b7;
margin-left:815px;
float:right;
}
[HTML] pobierz, plaintext 

i taki kod html:

[HTML] pobierz, plaintext 
<div id="leftmenu">fdgfhhfghfghfg fgh fdh fg hfdg hfh fgh f hf f f hfg hfgh fg hfdfg hfdgh  hfg</div>
<div id="rightmenu">fdgfhhfghfghfg fgh fdh fg hfdg hfh fgh f hf f f hfg hfgh fg hfdfg hfdgh  hfg</div>
<div id="centerblock">fdgfhhfghfghfg fgh fdh fg hfdg hfh fgh f hf f f hfg hfgh fg hfdfg hfdgh  hfg</div>
[HTML] pobierz, plaintext 

i wyglada to nastepujaca:

leftmenu centerblock
rightmenu


right menu ucieka pod left i center, dlaczego tak sie dzieje?