Solaris 8 Disk agent was last available with DP 6.21
Although not officially supported, there are some that, because of Application restrictions, are using different version of DP within the same cell
You would need to download the installation bits for DP 6 from the URL
and install the disk agent for Solaris, and import it into your cell
You would also need to make this Solaris a Installation server, so that you could download the patch bundle DPSOLBDL_00621 for DP 6.21, available at
http://support.openview.hp.com/selfsolve/patches
install it , and distribute it to your Solaris server