Remote PC not treated like local PC on main site lan

[killernet]

I'm having major problems with a remote Windows xp PC that needs to talk to a dos computer as if it is a local PC.

The VPN implementation I have used is as follows:

Remote Windows xp PC connected using XP client with static IP (within subnet) to a windows XP PC on the main site that acts as the VPN server.

Problem:

Although I can ping around the network from the remote PC the dos PC that it needs to talk to is not treating it as local and not allowing the remote PC to get the data for an application to work.

Please can someone advise on where this is going wrong, I would be tearing my hair out if I had any!

Thanks in advance.

Lawrence