IP access

[Szemerédy Gábor]

Hello list members!
We have a server with its public IP address and there is also a subnet
with
local addresses (192.168.0.x) on it.
We would like to limit the access from certain IP address so that it can

be
established only if the request comes from the same workstation.
Something like capturing the workstations MAC address to its IP address
,
so that the user can browse the internet only if the MAC address of the
workstation and the IP address are equal to the predefined values.
We do traffic accounting by IP address and would like to prevent using
the account of an other workstation by changing the IP address.
(In current situation one can browse the internet with certain IP
address and then
change the IP address and use the account of an other person).
Is there any solution?
Thanks