The lesson learned today is knowing a thing is quite different from being able to apply it- so in this case the thing I knew was that XML is CASE SENSITIVE and URL's ARE NOT so when trying to use this excellent trick for using the address of a site to filter a list http://vspug.com/maartene/2007/09/10/how-to-filter-data-in-a-data-view-web-part-based-on-the-url-of-the-web-part-page/ it didn't work- didn't work UNTIL I remembered that if my site address didn't match the case of the URL it wouldn't wouldn't work. To make it so that the filter parameter and the URL don't have to match for case I used a variation on this trick http://geekswithblogs.net/ranganh/archive/2005/09/12/53520.aspx
Happy day only 3-4 hours wasted.
