Preloading a rollover submit button?

[Kane250]

I'm using this code, which acts as a submit button for my form and is also a rollover. However, the rollover image does not preload and I don't think I can do it like I preloaded the other rollovers on my page. Can someone tell me what I have to add to this?

 

In my CSS:

.button {
border:0px;
outline:0px;
background:url('images/emailcheck.png');
width: 41px;
height: 33px;
}
.button-over {
border:0px;
outline:0px;
background:url('images/emailcheckro.png');
width: 41px;
height: 33px;
}

 

In my HTML

<input type="submit" value="" class="button" onclick="wopen('mainsub.php', 'popup', 400, 375); return true;" onmouseover="this.className='button-over';" onmouseout="this.className='button';" />

 

Can anyone help me out???

 

Thanks!

[Kane250]

bump for suggestions.

[Kane250]

nobody?