Changing Attributes Of An Existing Window?

I'm not really much of a javascript programmer, but I occasionally use javascript that I've found here and there. But I'm unable to find anything that helps me in what I'm trying to do now.

I regularly use a snippet of code that pops up a small window to display an image or a very small html file.Using the window.open() function, I'm able to disable scrolling, resizing, etc., and size it to my needs. I'll have a window.close link somewhere on the page. But in my current project, my customer's page has several links related to other companies. When you click on the link, an that company's ad pops up in a small window. At this point, the viewer can simply close the window, or they should be able to click on the ad and be taken to that company's website.

I'm able to have it close the window and open that new url in the parent browser window, but my website customer doesn't want their site to go away. They want the new company's website in a new window.

Or I can simply NOT close the popup window, but now the new company's website is in a relatively small browser window, unable to scroll, resize, etc. Is there a way for me to somehow modify an existing window with an onclick directive - something similar to the window.open() function, OR open a new browser window with window.open() AND close the popup window? If I haven't made myself clear, let me know and I'll try to explain myself better.