I have already have installed a openfire on my linux system and configured it with IM gateway plugin. Its really an wonderful app to work on with. I have install spark client and invited my friends (on LAN) to use my openfire server and spark client for ultimate IM experience.
Basically, I am a Java developer. I want to build a J2ME XMPP app, that can be configured with my openfire server and use yahoo IM services.
Well, i gave you the link to j2me jabber library (http://sourceforge.net/projects/micro-jabber/) which i think one can use to build his j2me client. Why do you need jabber and openfire if you want to connect to yahoo? Maybe there are libraries to connect to yahoo directly. I dont have anything else to suggest. Btw, there is a nice app which is working with openfire as is based on j2me i think - Nimbuzz. It also can connect to various openfire gateways (Yahoo also).