I take it that you want the new account to have its own inbox. You need to create a new folder in the Inbox.
To add a folder, on the File menu, point to Folder, and then click New. In the Folder name text box, type the name, and then select the location for the new folder.
You will then need to create a new message rule so that mail from the new account is directed to this folder. This is in Tools > Message rules.