I suspect it's the DSL filter causing the problem. There shouldn't be any filter between the dsl modem and the phone jack. If you're limited in the amount of phone jacks available, then you can buy a 1-to-2 or 1-to-3 Jack Adapter available at most electronic stores (Radio Shack, Best Buy, etc). This will give you two or three jacks to use, one for the dsl modem (without the filter) and the other for your phone/answering machine (with the filter in between). You can't connect your phone directly to your modem, but you can share the phone jack they use.
The purpose of the filter is to prevent your phone from interfering with the DSL frequency, which would cause reduced performance or connection problems without the filter, and to prevent the DSL frequency from interfering with your phone frequency causing audible line noise without it.
All electronic items (ie. phones, answering machines, fax machines) must have a dsl filter between them and the phone jack even if its a different phone jack in another part of your house (providing all jacks share the same phone line).
As for securing your network, you need to access the the modems firmware.
I would highly recommend you follow your modem's owners manual for this procedure.
Barring that advice, the following is generic information on how to access the firmware.
Most modem firmware can be accessed by opening a web browser and typing in 192.168.1.1 in the address window. You will be prompted for a username and password. The default is usually admin for the username and password or admin for the password. Once you have access, you should change both of these. Look for the menu for the wireless setting. You can change your network name from 2WIRE### to whatever you want by changing the ESSID. Once you do that your computer might disconnect the wireless link so I recommend you do this with a wire connection from your computer to the modem. Look for the security menu and choose the type of security (choices are either WEP or WPA). WPA is the stronger of the two and is unbreakable. Put in a security key (a type of password with a minimum of 8 to13 random characters and max of 63 characters). Once all is set, have your computer search for available wireless networks. Choose the one you created and it will prompt you for the security key twice. Once entered, it is stored in your computer and if done right it should show your connected to a secure network-WPA enabled.
I know its a lot to absorb but it's easier than it looks.
Again, I recommend you try your modem's procedure first.
Hope this helps.
