Here you'll find a pppoe hack of the Alcatel speedtouch usb modem driver.
Which enables the Speedtouch USB driver to support PPPoE with rp-pppoe, as some providers don't seem to support PPPoA. this patch is against the speedtouch-1.1 driver of
It permits the use of pppoe with the help of a virtual ethernet interface called tap0, to use this, you should make sure you have:
to install: you should patch your Speedtouch driver sources with a set of command like these:
cd /where/your/driver/sources/are
patch -p1 < /where/you/have/downloaded/the/speedtouch-1.1-pppoe.diff
make install
Next you'll have to: modprobe the tun/tap driver
modprobe tun
Then launch the modem_run as usual. (please refer to the original driver documentation to know how to dos this).
And launch the modified pppoa2 which will listen on tap0 for pppoe frames. eg:
/usr/local/sbin/pppoa2 -v 1 -vpi 8 -vci 35
Note that the modified pppoa2 will remain in the foreground. (this is test only)
Then you can start to configure your rp-pppoe package and when it'll prompt for the ethernet device where the modem is connected, you should specify: tap0

I'm not responsible if it fries your modem. This works for me.
I usually hang out on #ECI on theOpenprojects Irc Network with a nick flysomething.
Please report success or failure here along with the output of lsmod, dmesg and startmodem if you want.
sample output with my SpeedTouch USB:
ppp0      Link encap:Point-to-Point Protocol
          inet addr:  P-t-P:  Mask:
          RX packets:17719 errors:0 dropped:0 overruns:0 frame:0
          TX packets:13466 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3
          RX bytes:13641296 (13.0 MiB)  TX bytes:13005213 (12.4 MiB)

tap0      Link encap:Ethernet  HWaddr 00:FF:CF:F4:AF:93
          inet6 addr: fe80::2ff:cfff:fef4:af93/10 Scope:Link
          RX packets:17782 errors:0 dropped:0 overruns:0 frame:0
          TX packets:13546 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100
          RX bytes:14040045 (13.3 MiB)  TX bytes:13303858 (12.6 MiB)

root     21772  0.0  0.8  1392  556 pts/3    S    02:25   0:00 modem_run -m -f /usr/src/mgmt/mgmt.o
root     22213  0.3  0.7  1400  492 tty4     S<   03:06   0:05 pppoa2 -v 1 -vpi 8 -vci 35
root     22215  0.7  0.8  1412  500 tty4     S<   03:06   0:11 pppoa2 -v 1 -vpi 8 -vci 35
root     22217  1.6  0.7  1276  480 pts/3    S    03:06   0:24 /usr/sbin/pppoe -I tap0 -T 80 -m 1452
root     22221  0.0  1.4  2048  892 ?        S    03:06   0:00 pppd call dsl-provider updetach

About DSL
Auto-Configuration for the Connection between the DSL Broadband Network Termination (B-NT) and the Network using ATM
Protocol Independent Object Model for ADSL EMS-NMS Interface
Protocol Directory - ATM Encapsulation Methods
rfc2364 - PPP Over AAL5
rfc 1483 - Multiprotocol Encapsulation over ATM Adaptation Layer 5