Thanks for all your help. I have actually sorted the transparency problem now. I checked the page in
http://browsershots.org - a great tool by the way for checking cross browser compatibility - and tried a few things out.
At first the main problem was with ie 5 and 5.5 which are still used by a few people, so I wanted to make sure the iframes worked for people with those browsers. Turned out to be a simple case of forgetting to make the background of the source file transparent as well as adding the allowtransparency attribute to the iframe.
The iframe now works fine in ie 5.5 and although still not transparent in ie 5, at least it works (before the iframe did not show at all). I think transparency was only added with 5.5 onwards. Other than that, the only other browser that doesn't like the transparency attribute is konquerer 3.5.5.....and who uses that?!!
