PIX 506 problem : no traffic going through

Hi,
I'm recent to Cisco firewall config but having good network background in other topics.
We just purchased a  Cisco PIX 506E that we connect to our DSL modem to protect our LAN from Internet.
We have no need for inbound connection to our LAN so config is rather simple and standard.
According to the documentation and what I have seen on the web, that should be up rather easily but I cannot get it to work.
I have configure the interfaces, the pppoe connection on the pix following this procedure : http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_configuration_example09186a00801055dd.shtml

and the PIX shows the DSL connection is up and running.

However : from the PIX console, I am able to ping the Internet but from the workstations on my LAN behind the pix, I'm not able to reach the Internet.  The traffic between my workstations are not going through the PIX to reach the Internet.
My workstations have the PIX as default gateway and I have enable all ICMP traffic to pass through for testing but it is still not working.

What am I doing wrong ?

Here below is the config of the PIX :

Building configuration...
: Saved
:
PIX Version 6.3(3)
interface ethernet0 auto
interface ethernet1 auto
nameif ethernet0 outside security0
nameif ethernet1 inside security100

hostname pixfirewall
domain-name ciscopix.com
fixup protocol dns maximum-length 512
fixup protocol ftp 21
fixup protocol h323 h225 1720
fixup protocol h323 ras 1718-1719
fixup protocol http 80
fixup protocol rsh 514
fixup protocol rtsp 554
fixup protocol sip 5060
fixup protocol sip udp 5060
fixup protocol skinny 2000
fixup protocol smtp 25
fixup protocol sqlnet 1521
fixup protocol tftp 69
names
pager lines 24
mtu outside 1500
mtu inside 1500
ip address outside pppoe setroute
ip address inside 10.100.17.253 255.255.255.0
ip audit info action alarm
ip audit attack action alarm
pdm logging informational 100
pdm history enable
arp timeout 14400
global (outside) 1 interface
nat (inside) 1 0.0.0.0 0.0.0.0 0 0
timeout xlate 0:05:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 rpc 0:10:00 h225 1:00:00
timeout h323 0:05:00 mgcp 0:05:00 sip 0:30:00 sip_media 0:02:00
timeout uauth 0:05:00 absolute
aaa-server TACACS+ protocol tacacs+
aaa-server RADIUS protocol radius
aaa-server LOCAL protocol local
http server enable
http 10.100.17.0 255.255.255.0 inside
no snmp-server location
no snmp-server contact
snmp-server community public
snmp-server enable traps
floodguard enable
telnet 10.100.17.0 255.255.255.0 inside
telnet timeout 5
ssh timeout 5
console timeout 0
vpdn group pppoex request dialout pppoe
vpdn group pppoex localname myusername
vpdn group pppoex ppp authentication pap
vpdn username myusername password *********
dhcpd address 10.100.17.254-10.100.17.254 inside
dhcpd lease 3600
dhcpd ping_timeout 750
dhcpd auto_config outside
dhcpd enable inside
terminal width 80