I set up a VPN tunnel between 2 routers (Netgear DG834G & DG834GT) Connects successfully.

On the local LAN (address 192.168.10.0) I can ping the server on the remote lan (192.168.1.200) with a good response.

However, when I try to MAP a share from the remote server onto the Local machine I get an authentication box which none of my users (including the administrator) account are authenticated on, even though on the company LAN they all have the correct permissions to connect and modify these shares.

Why am I unable to authenticate as admin or any other user and how can I get around this.

I am using:
Client: XP Pro sp2 behind DG834G Router
Local LAN IP 192.168.10.3

Server: SBS 2003 (one NIC) behind DG834GT Router
Local LAN IP 192.168.1.200

All relevant ports and services are open on both routers, in any case the VPN tunnel connects without any errors.

i think it might be something to do wth the sever having on e NIC (network card) or something on the server not allowing users to connect via vpn, but am currently at a loss could anyone please help and advise if I'm missing something as I am currently

Not familiar with your server but you should check if it's security settings allow connections from different subnets. It's not impossible that the server is set to allow connections from it's own subnet e.g. addresses of the form 192.168.1.x assuming the mask is 255.255.255.0, but shut out anything from outside that range.

One possible fix would be to configure L2TP and make an L2TP connection to the remote LAN. That gets you an IP address on the same subnet as the server so you should be allowed in.