Difference between onMouseOver and onMouseEnter

You might spare yourself some coding by just adding :hover support for all elements in IE too:
try csshover.htc

Both onmouseenter and onmouseover fire when the mouse enters the boundary of an element. However, onmouseenter doesn't fire again (does not bubble) if the mouse enters a child element within this first element.

Unlike the onmouseover event, the onmouseenter event does not bubble. In other words, the onmouseenter event does not fire when the user moves the mouse pointer over elements contained by the object, whereas onmouseover does fire.

I always use onmouseover. I use onmouseover in the same purpose (highlights a row).