Upload several images to Google sites

You cannot add JavaScript directly to your Google Sites page. You can, however add a Google Gadget that has JavaScript in it. You can try the Google Gadget Builder. You may not get the result that you want, however, since your JavaScript is not valid. For example, your statements with (x)html elements will cause the JS engine to error.

var <strong class="highlight">images</strong> = new Array(  "image1.jpg",
        "image2.jpg",
        "image3.jpg");

It may work with E4X, but Google Sites is not rendered as XML. (Yes, it does have the XML doctype, but not the header, so it will not render as XML)

In addition to Google Gadgets, you can also try Google Apps Scripts. It allows for some server side automation.

There's a Select hyperlink up at the top which will bring up a dialog box, which will allow you to upload in batch. That way you can download all of the files onto your desktop from the other site, and then batch upload them to minus.

Hazarding a bit of a guess, I think what you are suggesting would be tricky due to measures against cross site scripting attacks. Dragging something over from another website probably wouldn't have the proper information coming along with it.