[Old Pedant]

Ummm...you are declaring this function to take *THREE* PAIRS of image names and image file names:

function roll(img_name1, img_src1, img_name2, img_src2,img_name3, img_src3)
{
    document[img_name1].src = img_src1;
    document[img_name2].src = img_src2;
    document[img_name3].src = img_src3;
}

But then when you *call* that function you only pass *TWO* pairs:

<a
onmouseover="roll(
    'sub1', 'http://images.bloomberg.com/r06/homepage/europe_home_tab.gif',
    'sub2', 'http://images.bloomberg.com/r06/homepage/HP_UKX.png')"
...

So why are you surprised that nothing happens in the third image???

Try again, this time passing THREE pairs.

But I don't understand why you WANT to change 3 images. Your first paragraph only talks about changing two images.