Everything goes fine until

Using ubuntu 10.4. Followed the directions here (http://omeka.org/codex/Install_on_Ubuntu) without any error messages. When I try to browse to http://localhost/Omeka, I get the following error messages and would appreciate knowing what I need to do to fix it.

Before installation can continue, the following errors must be resolved:

1.Archive directory not writable
The following directory must be writable by your web server before installing Omeka: /var/www/Omeka/archive

2. Archive directory not writable
The following directory must be writable by your web server before installing Omeka: /var/www/Omeka/archive/files

3. Archive directory not writable
The following directory must be writable by your web server before installing Omeka: /var/www/Omeka/archive/fullsize

4. Archive directory not writable
The following directory must be writable by your web server before installing Omeka: /var/www/Omeka/archive/thumbnails

5. Archive directory not writable
The following directory must be writable by your web server before installing Omeka: /var/www/Omeka/archive/square_thumbnails

The /archive directory and it's subdirectories need to be writable so that the derivative images have a place to go. It doesn't look like the Ubuntu installation page covers this, so check the regular Installation page, at the bottom look for the 4th bullet, which gives the commands how to do it.