>You could add a focus directive to the onload event of the body of one of the pages in the frameset (the main page, usually). Even after the focus is given to the login form, the focus should be given back to the page in the new window after it loads (put it in the page that takes the longest to load, if any). When you return to the login form, the cursor should be on the box you set it to before also.

Even by putting the focus as mentioned, the base page will take priority on the final process if a focus is activated.