Add class login to the username field. 
 Add class pass to the password field.  example: 
 <input class="login" type="text" name="user" value="" size="20" 
 <input class="pass" type="password" name="password" size="20" 
 style="width:100%" maxlength="15" /> 
 css:
Code
input.pass 
 { 
 background: url(http://ucozers.ucoz.com/images/Login_form_imag/010789ade8cd.gif) no-repeat; 
 background-color: #fff; 
 background-position: 0 50%; 
 color: #000; 
 padding-left: 18px; 
 } 
 input.login 
 { 
 background: url(http://ucozers.ucoz.com/images/Login_form_imag/584c3fe3b451.gif) no-repeat; 
 background-color: #fff; 
 background-position: 0 50%; 
 color: #000; 
 padding-left: 18px; 
 }