I posted some example code for this recently.
function enlarge (wURL, sp)
{
var specs = "width=800,height=600,top=30,left=30," +
"screenx=30,screeny=30," +
"resizable=yes,scrollbars=yes";
if (sp) specs = sp;
if (globalWin)
{
globalWin.close ();
globalWin = "";
}
popWin = open (wURL, "popWindow", specs);
popWin.focus ();
globalWin = popWin;
return popWin;
} I don't usually implement it with that global variable, but this is an actual example of a case in which I had an additional goal. This pops a full-sized image into an appropriately sized window when the thumbnail is clicked. Note that the window size (and other features) may be passed in. If they are not, a default set is used.
EDIT: As a matter of fact, you can see this in action by clicking the "Digital Paintings" link in my signature.