function filterSelect(e) {
    e = e || window.event;
    var target = e.srcElement || e.target;
    if (target && (target.tagName == "TEXTAREA" || (target.tagName == "INPUT" && target.type.toLowerCase() == "text"))) {
        return true;
    }
    return false;
}

document.body.onselectstart = filterSelect; //仅IE下有效

------解决方案--------------------

我借用下楼上的代码：
JScript code
function filterSelect(e) {
    e = e || window.event;
    var target = e.srcElement || e.target;
    if (target && (target.tagName == "TEXTAREA" || (target.tagName == "INPUT" && target.type.toLowerCase() == "text"))) {
        return true;
    }
    return false;
}
window.onload=function(){
   var o=document.documentElement?document.documentElement:document.body;
   var isFF=navigator.userAgent.indexOf("Firefox")>0;
   if(isFF){o.onmousedown= filterSelect}else{o.onselectstart=filterSelect}
}