First off check out
Bert's excellent thread to see the benefits of using SharePoint in your office. There was a tremendous amount of work put in to demonstrate the benefits with all the screenshots and diagrams, and I'd like to thank him for that.
People seem to be under the impression that you have to pay for SharePoint. SharePoint is free! You can install it on Server 2008, Windows 7, Vista, or XP. There's no need to get SBS Standard just for SharePoint. (Exchange is pretty sweet though). Obviously it's not as tightly integrated as it is on SBS2011, but it is functional. SharePoint 2010 Foundation is the same version included in SBS 2011. SBS Essentials people will not be able to install this on the server.
You can download SharePoint Foundation 2010
directly from Microsoft.