It sounds like what you want to do is put the modem into transparent bridging mode, which would cause it to just act like a modem and not have any other configuration. Just by googling I found some instructions on a forum for your model of modem, though I haven't tried it myself since I don't have one. I can describe to you the general process that you need to follow, since that's how I have my modem and router set up.
When a modem is in transparent bridging mode, you enter the ISP PPPoE information on the router, and it connects directly and transparently through the modem. The modem doesn't get an IP address at all and the external IP of the router is your internet IP.
internet <---> modem <---> router WAN port | router LAN ports/wifi <---> LAN
You would need to know your PPPoE DSL login information. It may be available in the modem's web interface, or you may need to call your ISP to get it. Once the modem is put into transparent bridging mode, you will want to configure the router with that information. The modem will no longer do DHCP, have a local IP, or anything of the sort - it will essentially be gone as far as your network is concerned, and your router will be the extent of your LAN. Make sure that the modem is attached to the router via the WAN port when you do this, not one of the LAN ports, otherwise it won't work.
Good luck, hopefully that helps you out. Make sure that you have access to a different internet connection somehow in case you make any mistakes so that you can come back to get help.
I'd been puzzling over how you could get it to work, when I remembered Connectify. If you can get your hands on a wireless USB it should work perfectly for your situation instead of having to deal with that router.
I'm not sure there's a good way to connect the router like that, there's too many variables between the Siemens device and the cable modem. You might be able to connect the cable modem to a LAN port in the router, shut off DHCP in the router, give the router a static IP that's on the same subnet as the modem but not taking the modem's IP, and see if it will route packets appropriately between your computer and the cable modem. If you don't even get DHCP from the cable modem, that's a bad sign. You could try setting a static IP address for your computer and manually assigning the cable modem as the gateway, but it might just ignore your PC if it doesn't go through DHCP first (I know mine does.) The router might get confused too if it's looking for WAN, so setting to bridged mode might help. It all really depends on how the cable modem and router operate, and I'm not sure how much of this is standards based. Might end up being a lot of trial and error...
Connectify though is really easy, but you'll need XP with SP3, and you'll want to run in Ad-hoc mode anyway.
Best Answer
Some things to try:
Software:
Telnet:
(according the product page telnet remote management is supported)
so try this in a command prompt:
If it's succesful you could use tst10 to create a script and add it to your scheduler (you could also test your connection in the script...)
Web interface:
differents ways: