[wp-hackers] Make WP permalinks ignore a directory?

[Alex Hempton-Smith]

Hey there,

I have a WordPress 2.5 install and I've just integrated bbPress, which is
installed into a '/forum/' directory.
When I visit '/forum/' the bbPress page opens fine, but when I open a thread
(/forum/topic/your-first-topic) I see a WordPress 404 error page.
How can I make WordPress ignore that '/forum'/ directory entirely?

Thanks!
Alex