PC access &ip-address range restriction

Hi all

I have setup windows 2000 domain server. I installed two NIC. I bound
one IP Net address 192.168 25.X to one NIC and 192.168.30.X Network
to other NIC. Both Subnet PCs can Login to my Domain server having IP
address 192.168.25.1.

The IP Network 192.168.30.X user can access other IP Network
192.168.22..X. I want to Block /restrict them to access any PC on
192.168.25.x Network. While I want to allow the user from 192.168.25.X
to access the Network 192.168.30.X

How can I achive this by using windows 2000 O/S features only. I want to
apply IP-filtering by using windows 2000 in-buit features.(Like group Policy ,
routing etc if possible)

Any reference on web will also helpful to me.

Thanks in advance.

ssp2000