passing value as querystring to a popup page

Hi,
On my page, i have a image which opens up a add comment popup page.
now on comment popup page,user can enter any comments & click submit or close button on the popup.
on submit,the comments entered shud be passed as querystring to the main page.
& from main page if user again clicks the image for adding comment then on the comments popup page, the previous comment entered shud be by default come in the textbox for entering comments.
how to do this??any help...
 
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