how is it not working?
in the accounts window when you hit Add do you not see Yahoo as a choice?
if thats the problem go to Plugins and load the libyahoo.so (prolly in /usr/lib/gaim or /usr/local/lib/gaim)
then try adding it.
also what version of gaim are you using? the latest is .59 and can be gotten from http://gaim.sf.net