I had an @home account for about a year. It was surprisingly reliable. My setup was dhcp but, for whatever reason, they never changed the IP. Also, the hostname they give your computer has a corresponding dns entry somewhere. So my old machine could always be accessed at something like "c12341541.brnfrd.ct.home.com". They don't want you to run a server on their standard service... I don't know if geeks running prototypes out of their appartments is a major concern to a big telecom like AT&T.
Unfortunately, your setup will probably different. As I recall, the way they setup the networking for cable modem is quite particular to the area.
If you're nervous about security of the box and don't know all of the ins and outs, using a home firewall gateway will help - most of em will let you open up ports to the outside. If you want to open up ssh to the outside, talk to someone smarter than me. I think there are some security problems with some versions. I notice intruders try to connect regularly via ssh to a test machine that I administer now, and sometimes I wonder if they've gotten in.
