There currently isn't a "Create new Workspace from open/selected tabs" feature. There are two ways you can get around this:
1. Select all tabs in the drawer you want to be in the new Workspace (command-click to make discontinuous selections) and either Command-X to cut them or Command-C to copy them. Create a new Workspace, click in the drawer to give it focus and then paste to load the tabs you cut/copied from the prior Workspace. Take your snapshot to preserve the new Workspace.
2. Open the Workspace manager and rename your current Workspace. Create a new Default Workspace to replace it. [Edit - I forgot to say that you should take a snapshot of the Workspace to preserve its state between sessions]
Edit: Hopefully, OmniWeb 6 will offer a better interface for managing Workspaces which will allow you to e.g. create Workspaces from selections, copy or move individual tabs from one Workspace to another in the Manager window, etc.
Last edited by JKT; 2007-05-03 at 10:41 PM..