Firstly, I would suggest you do a quick search of LQ with just "speedtouch" in the search criteria.
Now, also the speedtouch that I had (still got it, but its relegated to sitting on top of a pile of magazines - disconected) is the USB model not an ethernet model.
If it works like the USB one does, then after doing the search, try following some of the suggestions for stuff to check - I should point out, that I found it easier to list the files that I needed to check, opened them in "Kwrite" to see if they needed changing, if not, nothing, if they did, I highlighted them and after checking which needed changing, logged into root and changed them that way.
If, as you say its an ethernet type, then I would have thought that it would have most, if not all of the connection software inside it (most of them have some sort of access interface- the solwise SAR110
that I use now has a nice little browser based interface - though you may find that yours has a command line one).
Anyhow, if it's an ethernet device, then I would have thought that you are connected as a LAN, then you would need to make sure that you have the information for configuring that i.e. the modems internal IP number (I think that this would be called the gateway route or IP address), for the dialogue boxes that relate to that, and where you get a dialogue box for the DNS then you would have to put the IP number for your ISP, so the system knows to connect via them.
It is concievable, that you may well have to put these into the modem - but I wouldn't know, as I say, mine was the USB model and my comments above are a guess (judging from what I have to do to get my modem/router configured).
When you start digging through your search results, most of the stuff will relate to the "blue cow shit" looking model that is USB connected (don't rule out the suggestions), with some also refering to the speedtouch 330, which is the red/maroon more up to date version and some that mention ethernet models (the stuff to check out first).
Finally, check the linux config first as if you find that you have to change any of the modems internal settings etc it might affect your windows based connection (and you still need to connect to get further advice and ideas).
Speedtouch modems are OK when you get them working, but I changed from the usb one to the one I linked earlier, because it used to piss me off having to wait when it dropped the connection inbetween OS's and also because of the error
that I got meant that I had to re-install the OS and that REALLY pissed me off.
Hope this is some help (it's certainly all of the ideas and suggestions that I can think of), and whatever you do, don't give up - that's the easy way out.