Question : vpn connection issue

i've a problem connecting to VPN server in my office, the setup of the network is as follow:

My office: 1 x Aztech 600EW ADSL modem/ router
               running dynamis IP
               1 x SBS 2003 sever connect to the router
               serve as DC, DHCP, DNS
               6 x WinXp pro PC
               all PC were setup with Windows VPN client

When my office try to establish a VPN connection to my HQ VPN server, there can only be one session at a time.
Which means when #PC 1 has establised a VPN session with HQ, #PC 2 or rest of the PC wil not be able to connect to the VPN server. Error is 721 where the process hang at verify username and password.

The internet connection in the office is fine, i've test the VPN connection at other office and i can have more than 2 PC establish that VPN at the same time.

Is there any thing i need to set in order for me to let the client PC to have VPN session at the same time?

Answer : vpn connection issue

Site to site is quite easy to set up if you have similar routers (highly recommended) at either site as the information is basically the same but the IP information is reversed. The advantages of site to site are:
- all users can connect with bandwidth being the only limitation
- the VPN is already established when the client machines log on, making domain authentication and logon scripts possible
- much simpler as no connection has to be manually established by the user
- slightly better performance where the encryption is handled by a dedicated device
- site-to-site usually uses IPSec protocol rather than PPTP, resulting in better encryption
- no port forwarding to a VPN server is required so slightly better firewall security

Users can access the Exchange server in the same way. I have heard of a few issues with having to add a DNS entry for users to be able to access the Exchange server over the VPN, but that should be no different than using the VPN client.