I actually have been using a free program called "Trillian", that allows you to use three or more different types of messaging programs all at once.
MSN IM - mal [at] maljam [.] cjb [.] net
Yahoo/YIM - maljam2002
AOL/AIM - maljam2002
Yahoo/YIM - maljam2002
AOL/AIM - maljam2002
And, if you're anything like me, and can never work out those pesky world time zones and time differences, you need to check out the fantastic "World Clock".