I just use DSL on 1/12, and except for some testing in the beginning, it is pretty good. My plan is 7.1mb download
In my case of using my own router, I did this.
Change the modem to bridge mode (since the modem is actually a one port router), and disable the DHCP function.
In the router, use PPPoE, enter username and password, then you are pretty much good to go.
For those who use (or want to use) opendns, use dns-o-matic to do the update, since DSL's IP change like crazy.
I use the link wrt54gl router with the dd-wrt firmware. My modem is also 6100f.
I don't think you need to change the MAC address.
The downside of this is, since it is a PPP system (one point is the ISP, another point is your router), you will not be able to access the modem this way.