Day 984.b : Our Local Area Network Configuration and Troubles

Hi, I need a little networking help. 

Here is the layout of our noobie home network.


I am "Host 3". I run a dual boot machine: Windows XP and Ubuntu Jaunty.

When HOST 3 boots In Windows XP:

1. We can ping each other with some packets dropped.
2. We can see each other's icon in our workgroup
3. My computer (Host 3) cannot transfer files to and from other hosts
4. Hosts 1 and 2 CAN transfer files to and from each other
5. Host 3  CAN play network games (Tremulous) with HOST 1 and HOST 2
6. Host 3 has NO internet connectivity

When HOST 3 boots in Ubuntu

1. No connection whatsoever

*Some more information:

1. Host 1 acts as gateway, with 2 ethernet cards.
2. Host 2 can connect to the Internet using Host 1 as gateway

What I want to achieve:

1. Connect Host 3 to the Local Area Network using
    a. Windows XP
    b. Ubuntu

2. Connect Host 3 to the Local Area Network for the following reasons:
   a. File Sharing
   b. Internet Connection Sharing
   c. Network Gaming