The problem you are having is that the blog link (and most others) include the html as a link to only 'blog.php'. Since you are using
Vb integration that your problem is that outside the main
vb directory those links will not work.
to fix this, either edit the Template Navbar and make all the links absolute, for example if you have any custom ones then change them from:
mypage.php to
http://yoursite.com/forum/mypage.php.
For other plugins such as the blogs you will need to go to the Plugins Manager, find the plugin and edit the posbit section.
Want the easy way?

Then do this.
Take the attached file and rename it to the whatever file in the gallery navbar you are replacing. For example, mine is the blog.php file. Take the attached blog.txt and rename it to blog.php.
Then edit this file in a text editor. Change the two links to the links of your blog link and upload to your /gallery folder. This file will simply redirect the user to the right file. no editing necessary
Hope this helps, its what I do.
-Jason