Have you posted at 4theweb.nl? Micheal can usually talk users through the install.
I had an issue with this. The only way to get the paths into the configuration of the G2 component was to manually type them into the database using phpmyadmin. This is a bug.
Dreamhost puts your gallery album files outside of your www root. so something like:
home/username/gallery2_data (whatever you named it when you did the install)
The "full path" location of Gallery (the part installed within the www directory) would be something like: /home/user/domain.com/gallery/
Relative location would be either /gallery/ or ../gallery/
Mambo would be / or /mambodirectory/ (depending where you put it).
(don't forget those slashes!)