Shared Email Access - Is SBS the Answer?

I've got 8 users currently using a mix of Outlook and Outlook
Express. Over the years they have built up large email files
consisting of PDF's, JPG's, messages and other files for various long-
term projects. They currently have no true server, just a PC being
used as a file server/storage device. I intend to bring them all to
Outlook ASAP. A couple of the users have PST files in the 3 - 4 GB
size range. These files cannot be reduced in size and they will get
larger. A couple of the Outlook Express users have DBX files
totalling 3 and 5 GB.

We are looking for a way to allow them all to access one another's E-
Mail and associated files. Is SBS R2 the answer? Is there a BETTER

Thank you,