If you are using Microsoft Outlook (and not Outlook Express), go to "Tools > Email Accounts", select "View or change existing email accounts" and click Next. Highlight your email account and click "Change". In the next box, click the button for "More Settings".
In the next again box, click the Connection tab and select the option to "Connect using my local area network (LAN)".
See if that helps, it should prevent Outlook from trying to establish a connection itself to Tiscali. As far as CompuServe mail itself is concerned, there shouldn't be a problem although it is years since I used a CompuServe account. If you are on "CS2000", I seem to recall this was retrieved via IMAP4 rather than POP3, whereas CompuServe "classic" had POP3 access to its proprietary CompuServe Mail system.