cookies store usernames, if u have clicked the 'remember me' option.
outlook xprs stores the e-mail database in the folder C:\Documents and Settings\user account\Local Settings\Application Data\Identities\{...}\Microsoft\Outlook Express\ Windows and outlook stores them in the OUTLOOK.PST file, stored in the folder C:\Documents and Settings\user account\Application Data\Microsoft\Outlook\.. U can use a freeware 'password recovery tool' to find them.