How can I keep phpbb3 header while viewing gallery2

Hello!
I use both phpbb2RC1 and gallery2.
I have a link, in the phpbb3 header to the gallery.
Now, I'd like to be able to keep the phpbb2 header while browsing picture.
I do not need any account integration, only the header and the footer.
I'd like to keep this part:
[IMG]http://img458.imageshack.us/img458/2862/file81xsjrov1.th.jpg[/IMG]

Where should I modify something?

Thank you!

Yannick

ps: sorry for my poor english !