Short answer: if it is your production server: don't!
Never install chatting software on your servers.
If you still want to -- install Pidgin (a.k.a. GAIM)
- there are installation packages for all major distributions (RH, SUSE etc.)
- you can download it from:
http://pidgin.im
If you don't know how -- you probably shouldn't even try
There was an old (very old) version of Y!M for Linux, but the link disappeared somehow from the
http://messenger.yahoo.com page.
OTOH it had less functionality than Pidgin.