As og_gallery doesn't seem to work for me, I did this to the same effect. Not quite complete but looking for help on the last step!

1. Install CCK, views, imagefield CCK, imagecache, image api and organic groups (obviously)
2. Create a new node type with an imagefield. Configure this how you like.
3. Follow the imagecache documentation to set up whatever sizes you want - but also include a thumbnail size suitable for gallery views. Suggest 150x150px max and callign it "thumb".
4. Add a new view that provides a page, with the path "node/$node-group/gallery". Set view type to list view, and set a pager for how many pics you want on each page. I also set "provide menu" and "provide menu as tab" so it shows up in the group menu.
5. Set the fields to your imagefield you defined earlier. Here's where the imagecache magic comes in - in "option" select "thumb as link to node" (assuming that's what you called your small size). And the node title too if you like!
6. In arguments, set "og: group nids" to "display all values".
7. In filters set "node: type" to "image" (or whatever you called your image node type)
8. This will now give you an unordered list of all the gallery items per group. Now all that remains is to write a css style rule to make these show up inline rather than as a list.

Assuming your view is called "og_gallery"

Make views-list-og_gallery.tpl.php

<?php
  drupal_add_css(path_to_theme() .'/views-list-og_gallery.css');
  
  print $field_image_fid_label;
  echo "<div class='image_normalize'>";
  print $field_image_fid;
  echo "</div><br/>\n";
  print $title_label;
  print $title;
?>

And here's an example views-list-og_gallery.css

.view-content-og-gallery .item-list li {
  float: left;
  width: 150px;
  height: 100%;
  background-image: none;
  padding: 4px;
  margin: 3px;
  text-align: center;
  background-color: #eee;
}

/**
 * CSS rules to vertical and center align the image
 * http://www.jakpsatweb.cz/css/css-vertical-center-solution.html
 */

.view-content-og-gallery .item-list li .image_normalize {
  height: 150px;
  width: 150px;
  display: table; 
  overflow: hidden;
}

.view-content-og-gallery .item-list li .image_normalize a.imagecache {
  display: table-cell; 
  vertical-align: middle;
}

.view-content-og-gallery .item-list li .image_normalize img {
  text-align: center;
}

.view-content-og-gallery .item-list ul {
  list-style-type: none;
}

View an example