I have no experience on the tinnitus side of things, but I can recommend an online source for singing instruction. Check out the Singing Success program, and especially the Singing Success Online channel. The online channel actually had a few episodes that dealt with building the necessary skills to sing on pitch from the ground up. I found them very helpful and they improved my ability to stay on pitch tremendously.

I also agree with Gordon that you may want to see what a hearing specialist can do for you. Technology is great thing!

Best of luck to you and keep us posted on how things are coming along.

Take care,
Ty