I wouldn't have thought so as you would normally use the rj45 (network socket) which has a very different connector and different rate of transmission of data (so I believe).
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ADSL modems generally connect via USB or RJ45 network cables, I dont think any of them connect via firewire, why do you want one that connects via firewire?
you do know that those figures are in Mb/s whereas your adsl connection (512 Kb/s or 1Mb/s isn't).
Even a 'basic' ethernet connection at 100Mb/s is 100* faster than your broadband connection, so you'll see no difference between 10Mb, 100Mb and Gigabit ethernet or (if it were possible) your 400 Mb/s firewire connection.
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