Is it possible to share a VPN concentrator to support several customers. Homeworkers from several organisations will make contact to the same VPN concentrator, but need to be forwarded to different VPN's.

Yep, you would be using a Road warrior config. Host ---> Network The easiest VPN to setup is the Mircosoft PPTP server and client. 2000 server has the PPTP server, and every windows machine has the pptp client to connect to the PPTP server, but there are others VPN that you can use, in my opinion PPTP it's the easiest and quickest way to setup a VPN. PPTP can route IP and non IP protocols (IPX..etc) over a pptp tunnel IPSec however is strickely a IP tunnel, but it's much harder to setup then PPTP.

Not sure the previous post really answer the question!! Yes it should be possible to do it if the router support VLAN configuration. Netscreen routers can do both Vpn tunnelling and VLAN (virtual Lan).