You can connect a MyWireless modem to an Ethernet port using the special Ethernet cable using PPPoE. When you install the IPW drivers you are given the choice of USB or PPPoE, but I would guess that if you are having trouble with the IPW drivers in USB mode, the chances are quite good that you will also have trouble with them in PPPoE mode.
However, WinXP, and I'm sure WinXP 64 too, have PPPoE drivers built-in, so you can connect directly to a PPPoE compatible modem, so bypassing the IPW drivers completely. I haven't done this myself.
You will save yourself a lot of time and trouble if you just buy a cheapish 4-port router with PPPoE WAN port (e.g. ASUS RX3041 or D-Link DI-604) or a bit more expensive D-Link DI-804HV (with SPI) or DI-624 (with wireless)). Not only will you get a built-in hardware firewall, but you will also be able to share your internet connection between multiple computers, without have to worry about ICS or other sharing programs.