In Solaris, SUNWCuser is not a package, but a package cluster (the set of individual packages). SUNWCuser is always present on Solaris DVD as a list of individual packages.
You select the cluster when installing the system (SUNWCuser = ‘End User’ system) also you may boot from DVD and ‘upgrade’ system, selecting ‘End User’ system type (if you currently have ‘smaller cluster’).
Your current installed cluster is in /var/sadm/system/admin/CLUSTER file.
Each ‘bigger’ cluster also contains all packagse from ‘smaller’ cluster, they are ordered from ‘smaller’ to ‘bigger’, in this table: http://docs.sun.com/app/docs/doc/820-4042/preparecustom-100?l=ru&a=view&q=SUNWCuser