There are three different ways to offer OpenIDs, each varying in complexity.
One approach is to outsource account management and security to a third party. For many companies, this approach may be simpler and more cost effective. Janrain Identity Service is a software as a service offering that enables organizations to quickly implement OpenID.
Should you choose to host a solution yourself, you can apply one of the existing libraries, plugins or software packages that feature OpenID capabilities out of the box.
Lastly, and more challenging, is implementing custom support for OpenID in your software and account management tools. This approach may afford a greater degree of control over the user experience but it is also the most risky and only for developers experienced with web security. Start by reviewing the specs and documentation.