응용하시면 더욱더 좋은 소스가 될거 같네요.
[#레이어001_]<script language="JavaScript">
<!--
var win1
var win2
var chk
var moves

function gogo(){ //새창 두개 열기
chk = screen.availWidth/2
moves = 1
win1 = window.open('','','toolbar=no')
win1.moveTo(0,0)
win1.resizeTo(screen.availWidth/2,screen.availHeight)

win2 = window.open('','','toolbar=no')
win2.moveTo(screen.availWidth/2,0)
win2.resizeTo(screen.availWidth/2,screen.availHeight)
setTimeout("gogogo()",1000) //1초후 좌우로 열어줍니다
}

function gogogo(){ // 창이동 시키고 닫기
win1.moveBy(-moves,0)
win2.moveBy(moves,0)
moves *= 1.1
chk -= moves
if(chk>0)setTimeout("gogogo()",10)
else{
win1.close()
win2.close()
}
}

window.onload = gogo
//-->
</script>[_레이어001#]