If we're talking about 1.1 then look with FB at the RENDERED html to see if it can find icons. I've never had any problems with icons but wrong paths.
Re: 2.0. I'm not too big fan of development versions for production. Therefore I'll wait for Ext 2.0 beta[2-3] or Ext 2.0 RC[1-2] before I start to do anything leading to production with Ext 2.0. Meantime, I'm terribly busy these days, you can try if you want and you can post your experiences.
This is quite simple extension (compared to Accordion/InfoPanel).