No, AOL and Yahoo don't make their own client software for the N800.

However! There is a program called gaim that is a multi-protocol IM client that's available for Linux, Windows, and the N800. I haven't used it on my tablet, but have used the Linux and Windows versions several times. Nice program, and as I said, it's multi-protocol, so it can talk with AOL, Yahoo, MSN messenger, and others.