Thinking of buying a pre flashed modem - help

[jaded]

Hi guys, thanks in advance for any help. Im thinking of buying a pre flashed modem from ebay (infinite). The guy claims there is a good chance it will be plug and play if I can supply him with a working cable modem mac,a tftp-ip address and the NTL area (thats the easy bit) he can set it up. So, anyone have any ideas how I get this info? Questions:

1. Mac Address: I am on a 1mg NTL connection even though I dont have an account. I cancelled four years ago and it never went off. Can I sniff for a mac number using my own, current connection? My brother has a hooky modem (he lives across the road). I have read people mentioning 'borrowing' mac connection to sniff other macs. But I have also heard they cant be too close or something like that?

2. TFFT-IP: Can I determine this from my current cable connection? Obviously its going to be the same, no? Ive seen three or four different ones in the sticky, how do I know which is mine?

3. Is there any way the modem can be traced back to me? I know everyone has their own, unique ip address. Would I have someone elses ip or what is the situation?
Is there a unique id on the tags of every cable junction for example?

Cheers again guys