Separating Two Networks?

We have a T1 with a Cisco router.
On one of our public IPs, the Cisco is doing NAT for our main network
(200.1.1.0).

Off of the main switch, behind the Cisco, I have installed a Linksys
router - it is actually one switch off of the main switch. It is
connected to the main switch via another switch which is located
downstairs, connected to a drop which is connected to the main switch.

Off the Linksys router is a Win2K Server machine with the IP 192.168.1.
subnet 255.255.255.0 and gateway 192.168.1.1 - the Linksys is doing NAT
and port forwarding.

The Linksys has been assigned a distinct public static IP, different
from the static IP assigned to the WAN side of our 200.1.1.0 network.
On the Win2K Server, when I visit a website that tells the public IP,
it is the one assigned to the Linksys

For some reason the Win2K Server machine can ping machines (map drives,
etc.) on the main network, e.g., machines with 200.1.1. addresses - I
want know why? The machines on the 200.1.1.0 network cannot ping the
Win2K server's network 192.168.1.0.

I have subsequently turned off WINS, DNS, and DHCP servers on the Win2K
machine.

Is there some route in memory - the Win2K Server was formerly on the
200.1.1.0 network? Is it because they're on the same subnet - both are
255.255.255.0, or is it because they're really on the same network?

I was under the impression they would be distinct. I want them to be, I
was trying to test a VPN, but it didn't work because there was already
some common network.

Thanks for any clues.

-M