A nice feature of your Google Adwords account is that it supports collaboration with other users by allowing you to give them access into your account. Just one caveat to this is that any given account can only have access to one Adwords account. The following are the steps to grant a user with a gmail or Google Apps account access to your Adwords account:
Google Login Interface
Google Adwords Gear Icon
Google Adwords Account Settings Menu
Google Adwords Account Access Interface
Google Adwords Add User Box