Sharing secondary outlook calendar

My partner and I use Outlook 2007 on our respective laptops.

I use Outlook for my own diary and also have a second calendar, the latter
of which I need to be able to share with my partner.

I would like him to be able to view it on his laptop in Outlook and also
edit/add appointments which are then synced back to my copy.

Most of the solutions I've seen only allow him to view appointments, not
make any changes.

We don't have Exchange Server although the two computers are on a wireless
network.

Many thanks for any advice and suggestions.