Dunno where you got the idea of using PPPOE, because unless you've got cable tv from ntl or telewest, then it's gonna be a retail version of bt's adsl service.
That's pppoa ( aka pppoatm ) and not pppoe.
So, from memory (sorry, I got pissed of with my speed touch, the old turquoise cowpat looking one, about 12 months ago and now use a modem/router from solwise - it pisses all over any usb modem by quite a long way - I digress) - you will need to follow links to the alcatel site (alcatel/thomson or it could be under speedtouchdsl.com or something like that), you may have to fill in a small registration thing, do like I did and put any old shit in there, but then you should be able to download the driver.
If you're not up to speed with unpacking stuff, then search here at LQ (got an idea that there's something at the "tips n' tricks" section). But once unpacked, the bit you actually want is the mgmt.o file, that's the microcode, then you will have to copy it to /usr/share/speedtouch then it should be just a case of running the connection wizard. I would suggest that you select the "start at boot" option.
It always worked for me.
p.s. there's also more mandrake specific assistance here
(though you might not get an answer quite as quickly as you tend to here at LQ)