If the two can call each other and authenticate, then I assume your problem is connectivity? In general, this should work fine. As long as you have a dialer map configured on the 2500 for the remote Shiva (or a dynamic map will be created for dialin sessions if authentication is enabled) and a dialer-group, you should be OK. You may want to have a look at "debug ppp neg" to see that IPCP completes and both ends agree on the IP address of each other.
