Actually -- @Home rules vary slightly based on your cable provider. @Home is an internation company -- and in the US alone there are a dozen cable companies that have contracts with @Home. This of course changes continually becuase cable companies are continually buying out other companies ... for example TCI, or AT&T is always buying out everyone else.
In any case ... MOST of @Home does not provide static IP addresses, but "prefers" that you be set up statically -- this way they are free to change things on the network (splitting nodes, etc.) with out doing to much work like retaining IP addresses. What this also means ... is that even though most people don't have a "static" IP address, your IP address probably will not change for a long time - unless AT&T/Comcast/Insight ... whoever you MSO happens to be, do something in your specific local area as mentioned above (spltting nodes, etc.).
Some MSO's (AT&T is one of them) have started to "offer" static IP addresses... so that you can fill out a form online and supposedly your IP won't change, but only if you are running an OS that isn't compatible with DHCP. Hope this helps some. I have heard of one or two MSO's prividing static IP's at an additional chage - but I have also heard of those IP's changing also. The problem with this is that in the case of SOME MSO's... when you call @Home Tech support and tell them that your paying more money for a static IP... they most likly have never heard of such a thing... becuase local MSO's do it with out offering this service (seems that MSO's and @Home don't communicate there policies back and fourth as one would expect).
Hope this helps a little!