No, do not mess the ‘default’ email account (used to send files to Alwil Software for analisys, for instance) and the other Outlook Express accounts.
You can choose other email clients either… :
No, in Outlook Express part of the Mail Protection Wizard should be shown ‘all’ email accounts (in Windows 98). In Windows XP, as I have only one user, I’m not sure, maybe you can test.
Can you post that part of avast4.ini file (remove personal data, please).