PhpWebGallery user passwords are stored as hexadecimal MD5, ie 32 characters. It is possible that WordPress (and BBPress) are compatible with MD5 passwords but generate by default a SHA-1 password (40 characters). And PhpWebGallery is not compatible with SHA-1.

Which version of WordPress are you using?

(such an integration is very interesting to us, integration with WordPress is one of the big project once Piwigo 2.0.0 is released)

xphilippe wrote:

when the go live for Piwigo 2.0.0 is expected?

Before the end of February 2009.

xphilippe wrote:

And when the integration with Wordpress 2.7 is expected?

It's a project. So in the weeks after Piwigo 2.0.0 launch, we will discuss about how Piwigo and WordPress should be integrated. I don't know yet what implementation will result of this discussion. A plugin? A special build? Changes in Piwigo core? I don't know yet.

I didn't try WordPress 2.8 right now but I will do it asap.
Depending on what you are expecting I can give you some tips.
;-)