JavaScript not working on Mac. Pls help!

I've posted this on a dozen forums and still no luck. It's a small piece of code (2 lines!) and is causing a snafu.

This is the url:
URL

Basically: 2 iFrames.
Lower iFrame has row of thumbnails.
Top iFrame contains 'hold' image that *should* be activated when thumbnail is clicked.

Everything works fine on PC. No on Mac. If anyone can test on a Mac and knows JavaScript, I'd be extremely grateful.

This is the offending piece of code:
<script>
function click(clicks) { document.images['hold'].src="gfx/" + clicks; var nombre = clicks.substring(0,clicks.length-4); }
</script>

with this for the thumb:
<a href="javascript:click('apr_2.jpg')" target="hold"><img src="gfx/apr_2.jpg" width="83" height="50" class="imgBorder" alt="" border="0"></a>

when you say doesnt work, what does it do instead, and what error messages. im thinking some of the functions your using arnt suported by mac computers

Well, it just doesn't activate the 'hold' image. You click the thumb and nothing happens... can't remember the exact error message. The main JavaScript could very well be dodgy, it was taken from another site (a lesson learned!).

Actually, a Mac wasn't showing an error message (as far as I could see). Just wouldn't activate the 'hold' image.

Very confusing...

i dont have a mac, but i would say the javascript functions you are using dont work on macs

hmmm, could be. i didn't even think that JavaScript could differ between Mac and Win. but, hey it's possible!

some people think the iFrame is the problem. worst comes the worst, it will be a PC-only site!

It's probably not a Mac problem - it's probably a Mozilla/Safari problem.
Does the Javascript work on Netscape 7.1 on Windows? That's where I would start debugging first.