HOW TO SETUP OUTLOOK 2000 TO SEND AND RECEIVE MAIL FROM YOUR COMPUSERVE 2000 
MAILBOX.
NOTE: These procedures only apply if you have installed Outlook with the Internet Mail Only option. 
To determine your installation type, click on the Help Menu, click About Microsoft Outlook. 
In About Microsoft Outlook, you should see "Internet Mail Only" if you have the Internet Mail Only option installed. 
To change the configuration, click on Tools, Options, Mail Services, 
Reconfigure Mail Support, check the option next to Internet Only and click the Next button.
MORE INFORMATION
Like POP3, the IMAP4 protocol uses port 25 (SMTP) to send mail, but an IMAP4 
server uses port 143 to listen for mail. 
Unlike POP3, IMAP4 allows you to store your messages by default on the server, 
instead of downloading them locally. 
To configure Outlook as an IMAP4 client, follow these steps: 

Start Outlook, and on the Tools menu, click Accounts. 
In the Internet Accounts dialog box, click Add, and then click Mail. 

  Type a Display Name to identify your mail to recipients, and click Next.
  Example: John Doe

  In the E-mail Address box, type your e-mail address, and click Next. 
  Example: johndoe@cs.com

  In the "My incoming mail server is a" box, click to select IMAP. 

  Type the Incoming and Outgoing server names in the appropriate boxes, and 
  click Next. 
  Incoming: imap.cs.com
  Outgoing: smtp.cs.com
  NOTE: IMAP4 is a retrieval protocol. SMTP is still needed to send mail. 
  In the Account Name box, type your account name. Press the TAB key, type your 
  password, and then click Next.
  Example: 
  Account Name: johndoe 
  Password: yourCS2000logonpassword
  Click to select a Connection type. If you select "Connect using my phone 
  line," you will be given the opportunity to select an existing Dial-up 
  Networking connection or create a new one. For CS2000 select the LAN option.
  Click Next. 
  Click Finish. 
  Close Internet accounts box 
  Click Yes to download folders from the mailbox you added. 
  IMPORTANT! You must run the CS2000 program and make a connection before doing this.
  Click OK.

The following Microsoft Knowledge Base article may prove useful as well.

How to Configure Outlook 2000 with CompuServe 2000 Mail

PLEASE NOTE! There is an error in this article. Step 6 says:

"Type your CS2000 member name in the Account name box, type the password for your CS2000 account in the Password box, and click to select Log on using Secure Password Authentication (SPA). You may also want to click to select Remember Password. Click Next"

DO NOT SELECT LOGON USING SECURE PASSWORD AUTHENTICATION.