Does Windows XP Pro behind a Linux gateway running PPPoE cause disconnections?

It has taken me days to isolate this problem.

My Debian gateway (running kernel 2.6.12.2) repeatedly disconnects its PPPoE (over iBurst wireless internet) when I plug my new HP notebook running Windows XP into the network behind it. I am running rp-pppoe.so

The network is running on a 192.168.0.0 range and the gateway does NAT. IPtables clamps the MTU and MRU which is in addition set to 1432 (I've tried every number).

I discovered that when another machine running linux connects behind the gateway, there is no problem. The minute I plug the WinXP machine in, the PPPoE disconnects and tried to continually reconnect wihtout success.

My Syslog reflects:

Jul 10 12:57:04 server1 pppd[3097]: Couldn't increase MTU to 1500
Jul 10 12:57:04 server1 pppd[3097]: Couldn't increase MRU to 1500
Jul 10 12:57:04 server1 pppd[3097]: PAP authentication succeeded

*****
Jul 10 12:57:04 server1 pppd[3097]: peer from calling number 00:C0:EE:C3:XX:XX authorized
*****
Jul 10 12:57:04 server1 pppd[3097]: Cannot determine ethernet address for proxy ARP
Jul 10 12:57:04 server1 pppd[3097]: local IP address x.x.x.x
Jul 10 12:57:04 server1 pppd[3097]: remote IP address 196.30.31.100
Jul 10 12:57:04 server1 pppd[3097]: primary DNS address 196.30.31.193
Jul 10 12:57:04 server1 pppd[3097]: secondary DNS address 196.46.70.1
Jul 10 12:57:04 server1 named[1881]: loading configuration from '/etc/bind/named.conf'
Jul 10 12:57:04 server1 named[1881]: listening on IPv4 interface ppp0, 196.2.102.212#53
Jul 10 12:57:07 server1 pppd[3097]: Connect time 0.1 minutes.
Jul 10 12:57:07 server1 pppd[3097]: Sent 389 bytes, received 128 bytes.

Interestingly, the issue continues even when I drop all IP traffic from the internal network - indicating that some signal the WinXP machine is sending at an OSI layer below TCP is causing my woes. See the bold line above for evidence.

Could this be because my WinXP MTU has not been manually altered down? If so, hope do you implement a network behind a gateway without manually altering everone's MTU down?

My Debian gateway has two interfaces. One (eth0) is configured with no IP and that is connected to my iBurst terminal (wireless broadband). The other (eth1) is configured for a private 192.168.0.0 network. There is also a wireless card (wlan0) which I have disabled until I sort this out. Currently, the internal interface (eth0) is connected directly to either one of my laptops. When it is a Linux laptop, no problem. When it is the WinXP machine, the connection works fine (I ssh in, run VNC to the Linux box, etc) the PPPoE connections drop.

I thought it might be PPPoE deamons on the XP machine and carefully ensured these were off, so I don't think it was that.

AAAAAhhhh!