I think IE6 support can get skipped.

See countdown from microsoft:

http://www.ie6countdown.com/

If u use YSlow you see that there are 6 CSS Expressions.

Grade C on Avoid CSS expressions

There are a total of 6 expressions

• /js/jqGrid/css/ui.jqgrid.css

CSS expressions (supported in IE beginning with Version 5) are a powerful, and dangerous, way to dynamically set CSS properties. These expressions are evaluated frequently: when the page is rendered and resized, when the page is scrolled, and even when the user moves the mouse over the page. These frequent evaluations degrade the user experience.