You can use the Vacation Calendar on the http://companyweb intranet site that comes with Small Business Server or you can create a shared calendar in Outlook Public Folders.
1) Go to http://companyweb and select the Vacation Calendar on the left. You can add the calendar to your Other Calendars list by clicking on the Link to Outlook button at the top of the Calendar. The downside to this method is that the calendar is read only in Outlook. You cannot add items to the intranet Vacation Calendar in Outlook, you have to go to the intranet site and submit new items there. Method two is almost as easy and is fully editable in Outlook.
2) To make the shared calendar in Outlook, click the Folder List button at the very bottom left of the Outlook Window. This will display your entire folder list in Outlook. At the bottom of the list is Public Folders. Folders and items in those folders are accessible and editable by everyone (by default). Expand Public Folders, then right click All Public Folders, select New Folder, Choose Calendar Items, and give it a name. You can put it on your list of calendars by right clicking on it and selecting Add to Favorites. Next time you click on your Calendar it will show up in your Other Calendars list. Select it and it will display on a split pane with your personal calendar. Once it is created, it will show up in everyone’s Outlook Folder List under Public Folders, but they will have to add it to their favorites for it to show up on their Other Calendar list.