2007: Use a different master page for one content page

Hi everyone

I currently have a site with many content pages, and they all inherit
from a custom master page. I would like to attach one of those pages
to a different master page. In SP Designer, I select the page and go
to Format > Master Page > Attach Master Page and select the one I
want. It doesn't fail, but when I browse to the page it still looks
like the old master.

I've found the instructions at http://office.microsoft.com/en-us/sharepointdesigner/HA101671651033.aspx#3
and I'm doing everything listed there, but it's not working. I'm
probably missing something obvious, can someone help me out please?

Thanks
Chris

2007: Use a different master page for one content page

Just noticed something else:

When I open the content page in SP Designer, it's based on the correct
master page. However, when I open it in my browser, I get the old
master. I'm authenticated etc. and have ensured that the pages are
checked in.

Chris