Most users nowadays have two or more e-mails, how do they managed more than two. Typically by forwarding on e-mail to another e-mail address as a central hub of e-mails or using a e-mail client similar to Thunderbird or Microsoft Outlook. Subsequently, some users may have more than one screen name across different messenger programs. One way to manage being logged in to multiple screen names in different programs is to utilize a program that lets you chat on Facebook, AIM, Messenger, etc from one window instead of one for each.
Meebo enables the user to login to multiple accounts at once. Although there is an option to download a Meebo application for your desktop. I highly recommend using their web services Meebo Messenger to chat from your browser. The reason being that you will be saving space on your hard drive as well as reducing your computer security risk. Each program your install could have an unknown security hole as well as over time an accumulation of programs may make your computer sluggish. In addition, you will reduce the number or likelihood of installing toolbars which is another security risk.
Meebo is not the only program that allows you to chat from multiple accounts but the ability to use its services on web will add to convenience.
Meebo Messenger: http://www.meebo.com/messenger