Welcome aboard Guy, the pop up warning is only partially true. Most browsers and AV softwares are kind of reasonable about it, they only block pop ups that are initiated without action from the user
such as a body onload() handler. Most pop up windows initiated by links or form submits usually function just fine.
I'll skip all those though because a pop up will never work for this:
while the new window - or in some cases two new windows - can appear at the right, so that the user will be able to hop about between them by clicking.
When the pop up opens and the user clicks into the main window, the focus is now on the main window and the pop up will be behind
the main window and hidden. You won't be able to click back into the popup without moving or minimizing the main window. What you're really looking for here is modal content.
There are ways to do this without jQuery but jQuery has made it very easy. The content is already on the page, but it's hidden by CSS:
<p>Some visible content</p>
<div id="my-modal" style="display:none;">Some hidden content for the modal window</div>