How can I Introduce Javascript(?) while running xslt on xml file?

I am trying to process 1 single xml file;
Inside that xml file there is a <image> tag;
tag not contains any information about width;
I am aplying xslt on this xml.

how can i calculate the width..

My condition on html is...

if the width is <= 300 it will dispaly as is;
if the width is > 300 then their will be a popup on html page...

is there any way in xslt or should i have to use javascript;

if i have to use javascript then how can i implement the same...

<xml> file as below--

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="123.xsl"?>
<root>
<elements>
<element>
<image href="..."></image>
</element>
</element>
</root>

**** when i click on xml file, it will open in IE6.0 in html format ****

I am very glad if anyone help me....
I am strugling a lot on this issue....

thanks in advance..