hi, i 'm displaying gbk character in my ajax request.

HTML Code:
if (window.XMLHttpRequest) // if Mozilla, Safari etc
page_request = new XMLHttpRequest()
if (page_request.overrideMimeType) { 
    page_request.overrideMimeType('text/xml; charset=gbk'); 
the code above is used.

It displayed nicely in firefox. However, the characters in IE is not readable... It appears like '????'

After that, I've tried to remove the code below form the script:
if (page_request.overrideMimeType) { 
    page_request.overrideMimeType('text/xml; charset=gbk');
Then I added this code (page_request.overrideMimeType("text/html; charset=GBK") here:
if (bustcachevar) //if bust caching of external page
bustcacheparameter=(url.indexOf("?")!=-1)? "&"+new Date().getTime() : "?"+new Date().getTime()
page_request.open('GET', url+bustcacheparameter, true)
page_request.overrideMimeType("text/html; charset=GBK");
Same, it is ok in Firefox, but in IE, it keep display requestion content... nothing else is displayed. when i click on the next tab, it opens the targeted page in the same window..

can anyone please help to give some idea to solve this problem?