i'm almost certainly prejudiced, but I hold yahoo in the same regard as cockroaches...
I've managed to remove the toolbar (probably only nearly) completely, but the 'remove' just seems to deactivate it for awhile, and (unless they've changed it), nag you to reinstall it, and I've even have it just reverse my 'decision'.
I had to go in the the Registry and search for all the Yahoo entries, and delete them one by one. Seemed to take care of the problem, but I wouldn't recommend anyone who's not comfortable going into the Registry...
I never install anything from Yahoo...but that's me...if you want features, you can get Mozilla, and there's add-ons galore.
If you want training on Mozilla Firefox, Goodwill Industries (of all places) has a training course on Firefox. Plus, we can help if you need it.