windows ie6 and mac ie5 compatibility??

My javascript works fine under windows IE6 but doesn't do anything under Mac IE5.2. I'm using a lot of frames (with "parent" references) apart from that, nothing very complex!
Some code snippets pasted below. Any ideas gratefully received!!
===========
index.html
...
function training1()
{
if (window.open)
var t = window.open("index1.html", "", "resizable=yes");
}
...
===========
index1.html
...
<FRAMESET frameborder="0">
<FRAME src="main.html">
</FRAMESET>
...
===========
main.html
...
<FRAMESET COLS="225,*" frameborder="0">
<FRAME name="nav_bar" src="" scrollable="yes">
<FRAME name="main_page" src="main_page.html">
</FRAMESET>
<SCRIPT LANGUAGE = JavaScript>
h=new Array();
...
===========
main_page.html
...
<FRAMESET ROWS="*,75" frameborder="0">
<FRAME name="page_window" src="">
<FRAME src="button.html" scrolling="no">
</FRAMESET>
...

That's not very much to go on really; could you post a link to a page that demonstrates the problem you're having.

OK, go here:
http://myweb.tiscali.co.uk/dcorbett/training/2PM/RAMS/
and click the link. This launches a window with frames and content using my browser (WIN/IE6) but seems to fail when users with MACs access it. (Haven't got a MAC so can't try it for myself!).
Any ideas?