jQuery Grid Plugin - jqGrid

The jqModal script sniffs out whether the browser is IE (msie) and version 6.0 and if so, it uses position:absolute for the Modal overlay.  However, the script doesn't detect IE 8.0 running in quirks mode, which also needs to use the position: absolute, instead of position:fixed.  In IE 8, quirks mode, the function creates a new div at the top of the page and moves the rest of the content down (out of page view), instead of overlaying the existing page.

May want to consider using jQuery.support.boxModel instead of just browser version.  This returns false for IE8 in quirks mode, and true if IE8 is in standards mode.