Fitting window to larger image size.. How?

I've tried looking around but couldn't find any advice on this one...

When you click a product to get a larger image it opens in a new window.. That's just fine, but could the new window be fitted around the image so it isn't a full screen that pops up? (all my images are 600x600px)

I've downloaded the lightbox mod cause I thought that might be another idea instead of resizing the larger image, but th install makes no sence to me what so ever.. A step by step walktrough for dummies maybe? ;)

I think the file you need to edit to change the size of the pop-up window is:
/includes/modules/pages/product_info/jscript_main.php

The function is called "popupWindow(url)". Just change width= and height= to the dimensions you want to use.

I haven't tried the lightbox yet, so I can't help you with that one.

Changed it to this..

function popupWindow(url) {
window.open(url,'popupWindow','toolbar=no,location=no,directories=no,status=no,menubar=no,scrollbars=no,resizable=yes,copyhistory=no,width=600,height=600,screenX=0,screenY=0,top=0,left=0')
}

Nothing happened.. :no:

The first thing I'd do is look at the source code of the page in question and verify that your change is actually present in the javascript the page is loading.

If not, then you may have a jscript_main.php specific to your template; for example, if you aren't using the default template. If that's the case, take a look in:
includes/modules/<your template>/pages/product_info/
and see if there is a copy of jscript_main.php there. If there is, make the change in that file and re-test.