Thanks for all replies so far. Here's photos.
All advice greatly appreciated.

Photo of existing trim:
http://i899.photobucket.com/albums/a...psyltoqucn.jpg

Photo of existing recessed light without trim:
http://i899.photobucket.com/albums/a...psjkjq6lzy.jpg
http://i899.photobucket.com/albums/a...psqfuelsvu.jpg
http://i899.photobucket.com/albums/a...pscfgaxacv.jpg
http://i899.photobucket.com/albums/a...psqryhsb7w.jpg

Photo of what I _want_ to install (which doesn't appear to grab hold of anything inside the recessed fixture):
http://i899.photobucket.com/albums/a...psofmuph3q.jpg