How to process div pop up window?

[Lily Yuan]

Hi,all
I open one browser,go to a web. And there is a link in the page, when I
clicking that link, it will pop up a new page(the old one not close),and
I will do some operation on the new page.I try many methods, but can't
do the operation on the new page.
could you help me with out it? or could you give a div pop up sample?
thanks

this is html of the link
<div id="googleGeo">
<ul id="geos">
<li class="header">
Geo
<a style="display: inline;" class="PopUp"
href="/geotarget_display/">add Geo targets</a>
</li>
</ul>
</div>

new page url: http://corduroyapp.com/campaigns/geotarget_display/
new page title:RG Geo Targets

this is the checkbox that I'll set:
<input type="checkbox" id="Canada">