I see where you're going, and that's part of another way of installing. You want to ignore Seaside repository on
squeaksource.com unless you get a few things first. The way I'm describing wants you to go to
squeaksource.com/MetacelloRepository. Then you see lots of ConfigurationOf*** files. Load the one you want. Open a Workspace. Type "ConfigurationOf*** load" then do it. Seaside3.0 takes easily seven minutes to load. Then in a workspace type WAKom startOn: 8080 and then do it. Then go to localhost:8080/seaside and you'll see the browse page.
They should have answers to all your questions including the method you tried first. If there's any problem with those videos or instructions, please let me know.