Preload Image Script

[dog]

Hello,

I'm using CSS to create a rollover effect, as shown below:

a#menuAgencia {
  background-image: url(menu-agencia.gif);
}

a:hover#menuAgencia, a:focus#menuAgencia {
  background-image: url(menu-agencia_ro.gif);
}

I'd like a script to preload the rollover image.

Any help is much appricated.

Thanks,
dog