Thanks for your comments! Submitting to the gallery now.
I did manage to have the whole site validating fine but my clients webhost use a form of PHP setup in safe mode (if I remember correctly) that creates session ID’s for each visitor which inserts all those ampersands and strings of numbers after every link creating validation issues. Their server policy and PHP setup also stops me from using friendly URLs which I was really keen to do. Still - can’t have everything!
Looking at the package you suggest now.
Thanks again

Stef
***EDIT***
I managed to fix my validation problem with the help of Google and adding the following line to index.php
ini_set('arg_separator.output','&');
No use of &xhtml plugin needed. Thanks though for giving me the impetus to go and sort out the problem AMDbuilder

I’m happy now that everything validates again.