Joining the DDR question....

There are two commands involved. dialer-group and dialer-list.

dialer-group x where x is a number, is applied to the interface in question. then in standard config mode the dialer-list command specifies an ACL eg

dialer-list x protocol ip list 101

then you have an access list which actually defines the interesting traffic

eg

access-list 101 permit tcp any any eq 80

so that list will bring up web traffic. So long as there is enough web traffic crossing the link to stop the idle-timer timing out the link will stay up. idle timer is set on the dialer interface with

dialer idle-timeout x where x is in seconds.

I'm sure cisco can put it much more succinctly!