ADSL, Proxy & Bridge

[Jhon Ramawi Putra]

Dear Gurus...

May be this is a beginner question, but any help will be appreciated.
This is existing my network diagram:

(.....Internet.....) --- [ADSL MODEM]-----[LAN Switch] ---- Desktops 
(192.168.0.1, etc....)
                      192.168.0.9 

The ADSL Modem act as gateway.

Now i want to configure my network to be like this:

(.....Internet.....) ---[ADSL MODEM]
                ip : 10.0.0.1, net mask : 255.0.0.0
                        |
                        |
                eth0: 10.0.0.2, net mask : 255.0.0.0
                [Computer A] 
                eth1:192.168.0.10 netmask : 255.255.255.0
                        |
                        |
                [LAN Switch] ----  Desktops (192.168.0.1, etc ... with 
netmask : 255.255.255.0)
 
The ADSL Modem is attached to Computer A via eth0. Then my eth1 is 
connected to LAN. I want to make Computer A as Proxy Server .

Then i tried to make a  "bridge" using brctl, and followed every step in 
"How to" documents that i found from googling, but i got no success. 
Computer A can ping to LAN Clients dan Browse to Internet. LAN Clients can 
ping Computer A, but they can't ping The ADSL Modem and browse internet. 
So, i assumed that the bridge didn't working well.

If bridging works, i planned to install Squid dan configure Ip Tables.

Can anyone help me how to solve this problem...? Or point me to a 
comprehensive tutorial about this... configuring a computer to be a proxy 
server using ADSL Modem.

Any help would be greatly appreciated.....!!!

Best Regards,
Jhon Ramawi Putra