Thanks to Forumotion Help, who taught me CSS in a matter of minutes, I was able to create this code off of a code that they started, like, 2/7 of the way through! YOU'RE WELCOME, FORUMOTION.
Bunch of lazy...*murmurs*
Yeah, anyways, a lot of thanks to them.
Here it is:
#i_icon_mini_index {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_index:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}

#i_icon_mini_portal {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_portal:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}

#i_icon_mini_calendar {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_calendar:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}

#i_icon_mini_gallery {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_gallery:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}

#i_icon_mini_faq {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_faq:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}

#i_icon_mini_search {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_search:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}

#i_icon_mini_members {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_members:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}

#i_icon_mini_groups {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_groups:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}

#i_icon_mini_profile {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_profile:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}


#i_icon_mini_message {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_message:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}

#i_icon_mini_new_message {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_new_message:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}


#i_icon_mini_logout {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_logout:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}


#i_icon_mini_login {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_login:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}

#i_icon_mini_register {
background-image: url();
width: 105px;
height: 135px;
}
#i_icon_mini_register:hover {
background-image: url(IMAGE2);
width: 105px;
height: 135px;
}

Remember to change the sizes.
Oh, and here's the source: http://help.forumotion.com/manage-the-appearance-of-your-forum-f45/navbar-rollover-image-t77022.htm
"Navbar Rollover Image."
Oh, and shortly after this message, the navbar will have rollover buttons.
ALSO, IMAGE1...I forgot to put those back...