The IOpener service is discontinued, so there's no email or content available for updates. AT&T and EarthLink gave it a try after Netpliance folded, but I think they gave up on this as well.
It's certainly possible to hook up the IOpener's modem to one connected to another PC. While I've used Linux on the PC, it should be nearly the same process for a Windows server. The Internet Connection Sharing stuff in Windows should get you started. There's also a very good document in the Tech Reference section that describes the process. The general idea is to disable the "Wait for Dialtone" on the IOpener's modem, force the Windows PC to answer the modem ("ATA"), and then have the IOpener dial.
I used the process to hack into the "AnyISP" Sandisk image and add some debugging backdoors a couple of years ago. Originally, I was going to produce a Linux image as an ISO distribution. My idea was along the lines of the cable-modem uncapping procedure -- create a Linux host PC that the IOpener could connect to (via the modem technique mentioned above), and then spoof Netpliance's servers to trick the IOpener into installing the AnyISP software updates. It's all there in the Sandisk image, just need someone with the time and determination to cobble something together.
Sadly, I moved onto other projects soon after the backdoors were added to the AnyISP image, and I never got around to completing that hack...