In other words, using this module, you can assign the role "contributor" to a user in a group, and the user will only have the permissions of that role while he is in that particular group. 

This module does not affect other site-wide roles assigned to the user.

Installation

Unpack in your modules folder (usually /sites/all/modules/) and enable under Administer > Site Building > Modules.

Here are some key features of "OG User Roles":

· Assign a default role to all new users who sign up to your site.
· Allow group admins to define default roles for signups to their groups.
· Notify group admin of new group subscribers. Requires mimemail.module.
· Set a default "Founder" group role for users who create groups.
· Set a default group administrator role for users who are elevated to group admin status.
· Set a default group role for new subscribers to a group.
· Create subgroups.
· Create and use registration codes for automatic subscription to groups.
· Comes with it's own access control for optionally integrating the taxonomy access control (TAC) and organic groups (OG) modules.
· Disallow all Public Posts.
· Supports Content Access and Access Control List access control modules.
· Works with OG Vocabulary module.
· Works with modr8 module.
· Patched for compatibility with Relativity module.
· Compatibility with Content Type Administration by Organic Group module.
· Optional settings and user.module patch to reset user_access() permissons cache
· Configuration option allows Group Admins to approve new site signups for groups they are admin for.
· Hook provided to allow other OG modules to easily supply Group Node ID.
· Access control for Multiple Node Access.
· Provides block for Group Logo.

Requirements:

· Drupal 5.x
· Drupal Organic Groups module