Receptional_Andy - 8:28 pm on Nov 24, 2008 (gmt 0)

I'm 99.99% sure that these PHP session ids are not being generated by my site

IMO it's still worth checking see it's an easy test - just view the site with cookies disabled. Another way would be to view the Google cache of an indexed URL with a session ID in it, and then see whether the other links on the page also have a session ID appended.

It seems unlikely that another site has linked to your pages with session IDs appended, although anything's possible ;)

The htaccess code looks fine, and will work if your host supports it. It will not, however, remove URLs from Google's database.

Removing pages with session IDs is best achieved by (permanently) redirecting those requests tp the same page, but with the session parameter removed. You can see examples like this one [webmasterworld.com] over in the Apache forum. Note that even if you stop session IDs being generated, and redirect requests, such URLs can hang around for a long time, since Google is unlikely to request them very frequently - so doesn't discover your redirects very quickly either.