2003 server: File sharing beetween ICS and LAN

Hi,

I have a Cisco ADSL router:
192.168.254.1 (Gateway)

I then have 2 computers connected to it:
192.168.254.2 (fixed IP)
192.168.254.3 (fixed IP)

Since this router would allow max 4 connections, I dedicated my win 2003 server (192.168.254.2) to do ICS, using a second NIC:
192.168.0.1 (2nd Gateway)

Behind this ICS are connected 5 computers:
192.168.0.2
192.168.0.3
192.168.0.4
192.168.0.5
192.168.0.6

All computers access the Internet correctly (My ISP would probably be furious but I don't care, it isn't contractual)

The W 2003 server (with 2 NIC cards) can see files on both LANs.

Any 192.168.0.* computer (including W 2003) can see file on each other AND files on 192.168.254.* computers but slower

Any 192.168.254.* computer (including W 2003) can see file on each other.

BUT no 192.168.254.* computer can see any 192.168.0.* computer

Since 192.168.0.* computers can see 192.168.254.* computers, there should be something to do to allow 192.168.254.* to see 192.168.0.*, No?

I don't want to put my computer (192.168.254.3) behind the ICS because the Cisco router forward ports to me that way and I cannot change Cisco configuration, and also because I want a better access than other computers who have to share alf the total bandwith.

Any advices?

Thanks!