Well I don't believe your going to be happy with 3com or your internet service provider, I would be very upset with both. First of all 3com is not and will not support Linux drivers for your cable modem or any of the ones that they already didn't have a linux driver for. This is because they have discontinued all support for their cable modem line as of August 10th, 2001.
Which means if something happens to your modem or whatever they won't help. Which also means your ISP SHOULD NOT be using this modem. What I recommend you doing is calling your isp and saying you want an external modem that supports Linux. That you know they are distributing an unsupported modem to their users. If they don't, I would demand a refund and wait for DSL. This is just what I would do though. What would piss me off the most is that from what I could find, people have been asking for these drivers since middle of '99! Your ISP REALLY shouldn't distribute an unsupported and discontinued modem.