To clarify some things:
1) I clicked on 'Bridge Mode' in the modem setup, and then "Apply". This made the home modem screen stop displaying "PPPoE 8/35" and changed it to "RFCSomeNumber 8/35". However, now that it says that RFC thing, I cannot get on the internet. Resetting to factory settings does not change anything; I need to get that setting back to PPPoE 8/35.
2) My modem had port forwarding stuff already there. I just had to add the appropriate entries, and here is why:
For example, take Starcraft. SC needs to have TCP and UDP ports 6112-6119 forwarded. So I told my router to forward 6112-6119 to my PC. This did not allow SC to work correctly; the ports were still not being forwarded. But when I also added forwarding entries to the modem, THEN it worked fine. I had to tell the modem to forward to the router, then have the router forward to the correct computer. So I don't know what most 5200s are, but mine is most certainly not in dumb mode by default, and now it will not work at all b/c it is in bridge mode.
My router is an IPCop machine, fyi. But it is not the problem; no matter what ports I forward with the router, I also need to have the modem forward them as well. This holds true for my replacement modem, a 5667, as well.
Any help on how I can get the 5200 working and have it work in "dumb" mode, so I don't have to tell it to forward ports and just have it forward everything, would be much appreciated.