Mouseover effects require special handling to be fast enough. There are two global functions available just for this purpose (see /lib/system/html.js):
function mouseover(element, name){...}
function mouseout(element, name){...}
The first one adds a CSS class selector 'name' to the HTML element, the second removes it.
To create mouseover effect you have to define a CSS class:
<style>
.active-row-highlight {background-color: yellow}
.active-row-highlight .active-row-cell {background-color: yellow}
</style>
and add the following script
var row = new Active.Templates.Row;
row.setEvent("onmouseover", "mouseover(this, 'active-row-highlight')");
row.setEvent("onmouseout", "mouseout(this, 'active-row-highlight')");
obj.setTemplate("row", row);
This is slightly different from normal syntax - where you supply a function as an event handler. Here instead of a function you provide a string which is simply assigned to HTML element "onmouseover" property and is evaluated on mouseover event.