...máš tam chybu v šířce...#menu :



*{margin:0;padding:0 ;}
body{ text-align:center;margin:0;font-family:arial; font-size:11px;color:#CCCCCC}

#right_main_border{ background:url(images/b_right.jpg) repeat-y right;;width: 699px;text-align:left;margin:0;}
#left_main_border {background:url(images/b_left.jpg) repeat-y left;width: 699px;text-align:left;margin:auto;}
#bottom{backgr ound:url(images/bottom.jpg) bottom center no-repeat;width:699px;height:48px;margin:auto;}
#m enu{background:#00FF99; height:40px;width:500px;float:right;text-align:lef t;float:right}
#main_left{background:#993399;float : left;height:500px;margin-left:7px;width:190px}


. . .taky bude jednodužší použít "float:left" na "main_left"