No problem, I am presently surfing with ADSL 96kB/s downstream and 16kB/s upstream.
You need a standard network interface card (in my case a 3com905) and a standard DSL-modem which has to be connected to the NIC. The DSL-modem is operating system independent, i.e. does not need any driver or software configuration.
There are also solutions with USB DSL-modems connected directly to the USB-port without a NIC. However, these modems need special drivers (normally only available for Win) and they are a little bit more expensive than a NIC and a standard DSL-modem together !
DSL uses the PPPoE protocol. There are at least 3 different software packages (payware) for this: Safe Fire, InJoy and ISDNPM. The latter is bundled with eCS 1.1 .
More infos can be found here: