I share a DSL connect to 4 machines around the house. Very similar setup, I actually had the lan first then added the connect to get them all online.
There should be no problems, might have to call your isp a time or 2 to figure out the details but its really not that hard.
I've had steady flying while my wife surfs, my daughter downloads music and my little p133 testbed machine does seti@home sets.
Granted for TOD's I tend to ban everyone from the room but mostly for concentration not fear of connect woes.