Install OG, Date Field and Views. Create a Group called Event, assign it a Date Field. Setup the privalages (get the DEV Version). Then allow members to join the events. And use Views to display the groups and the members that belong in that group. You shouldn't need any custom code and it will work in Drupal 7. There is allot of flexibility in OG 3.x

Create a "Group" named "Event". You don't need to install all of the OG modules, just a few. You dont need to create a group content type: you simply need an "Event". 
People create Events and join Events. Go into group default permissions and make the group public by allowing people to join the event without subscribing.

You may want to use the "String Replace" module to easily customize some of the language to your liking, or over-ride the group theme functions. "String Replace" is simple and fast, but can be a bit too universal (it's up to you). Either can help make the language of joining to be just as you want. The template over-ride will allow you to make additional changes to the user interface.

Use a view, and a custom template.tpl.php! Done! Its fast, light weight and easy. Users will never know they are joining a "Group" and the results you get will exactly match what you want. Easy as PIE!