If the HDD is fresh and never been formatted before (not sure about Solaris 8) but in Solaris 7 after you go through some basic install steps it'll place you into the prompt and from there it's easy as.

#format
Then select label the disk (Option 4 off top of head)
once HDD is labelled then you can verify it's done

Right click on screen and select restart install and it'll pick up from where it left off.

(If this is wrong well it's 0200 here and I'm not thinking straight)

As for the slices and how you want to partition the disk it'll ask you in teh format. Normally right near the end. You can select auto partition or manually partition your drive.