CSS Positioning help ( sprite )

The former css is like this:

.menu-item-5 {
 	background:transparent url(images/home-icon.png) no-repeat scroll 50% 5px;
	}
.menu-item-8 {
 	background:transparent url(images/Windows-icon.png) no-repeat scroll 50% 7px;
	}
.menu-item-9 {
 	background:transparent url(images/mac-os-icon.png) no-repeat scroll 50% 6px;
	}
.menu-item-10 {
 	background:transparent url(images/driver-icon.png) no-repeat scroll 50% 5px;
	}

I works all good, but I change it to like this:

.menu-item-5 {
 	background:transparent url(images/noicons.png) no-repeat scroll 0 -96px; width: 40px; height: 39px;
	}
.menu-item-8 {
 	background:transparent url(images/noicons.png) no-repeat scroll 0 0; width: 40px; height: 36px;
	}
.menu-item-9 {
 	background:transparent url(images/noicons.png) no-repeat scroll 0 -145px; width: 40px; height: 40px;;
	}
.menu-item-10 {
 	background:transparent url(images/noicons.png) no-repeat scroll 0 -46px; width: 40px; height: 40px;;
	}

The icons shows correctly but the menu button looks in a mess. Any help appreciated!