Goto your computer. click on make a new connection (Not sure how win 98 is set up compare to Xp, its been a while)

Make a new connection , fill in name (maybe as MSN 1 or what ever) then fill in dial up number and password and user id.
Click finish.
Now remove connection that your Msn has been dialing with and use the new connection.
(Actually once the old one is removed the new connection will be your new default)

Now click on your IE or Netscape and the new connection will pop up aksing for password (if you don't want your computer remember it) and that should do it.