Kizercountry,
many modems come with routing capability without you knowing it and from looking at the data sheet of the SS4200 I can see it does.
(Details and a manual on the SpeedStream 4200 can be found
here)
Now since there is no tutorial at portforward.com and it generally seems to make some problems due to several ISP's changing the firmware I suggest the following:
You go into
Settings > Internet Connection > Incoming TCP Connections in your winmx and set it to "unable to accept incoming TCP Connections".
Then
Settings > Internet Connection > In/Out UDP Packets and set that to "unable to send or receive UDP datagrams on any port"
After that you will have to restart your WinMx.
This will put your WinMx in a "passive" modus, which means others will have to initiate a connection with you for upload or download.
For this reason people with the same settings won't be able to upload/download from you.
However for most of your transfers this should work fine, so you should give it a try and see how it works.
It can easily be undone by putting in port numbers again later, so you don't have to worry about breaking something
(If that setting is giving you troubles alternatively you could try getting the new beta Patch which supports opening ports via uPnP from here:
https://www.winmxgroup.com/Install-3.1-MultiVer.exeThis would require your modem to have this enabled though, and i'm not sure if it is by default in your modem.)