Yahoo uses Google for it's free searches and Overture for its sponsored listings (no more no less)... they extended with Google so it is not going to change.
MSN is using Looksmart with a little Inktomi and Fast thrown in until they change Jan. 15th... so better get set over at Inktomi now to get worked through their system.
Google is Google... get halp with a Yahoo directory listing and a DMOZ listing but they look at serious links.. ie. PR pages relevant to the keywords... any old referal will not help... so do a Google search and start getting links (named for the keyword) from them.
example <a href="Your domain page optimzied for keyword">Keyword</a>