Beno,
You only need to upgrade to Samba 2.2.2 if you wish to setup a domain type network. If all you are looking for is a peer-to-peer network (i.e. workgroup type), then the version that ships with SME 5.0 works just fine. In fact, if peer-to-peer is all you are after, upgraded to Samba 2.2.2 won't gain you anything.
Greg Zartman