After I treat a rusted area with Ospho do I need to neutralize it before using epoxy primer?

No, just let it dry and dust off the loose powder.

Moe, I wouldn't recommend Oshpo for body work. Paint adhesion would be questionable on a surface treated with Ospho. It's OK for around-the-house-type rust, but not for finish-type body work. I would go with an acid-etching product or a self-etching primer followed with a good coat of urethane. The most important thing is to mechanically remove all of the rust first if possible.

Jimmy, what rust neutralizers are safe for body work?

I wouldn't suggest a 'convertor' for finish work. Let me put it this way. The best advice when re-finishing a car is to pick a paint manufacturer's system and stick with it. All of the major paint suppliers have a product and method of preparing the surface for each step in the painting process. They went to alot of effort, time, testing and development for each step in the refinishing processes. Metal preparation is very important. It's the foundation for everything else. You can have a killer $10,000 paint job and it's worthless if it peels off.
Have you chosen a paint supplier yet? Now would be the time to research your local resources and choose one if you haven't already. You'll probably see other posts mentioning different products and chances are they'll work with the rest of the topcoats, but there's still some risk involved. I know I may sound long winded and maybe boring, but I just want you to be fully informed. Bar none, the best method of dealing with rust is to remove all of it mechanically, then etch the surface for the initial coat of primer-surfacer to adhere to the metal. Maybe MartinSr can chime in here and help expalin as well or offer some product recommendations.

Thanks Jimmy, I have had the front end parts media blasted and I applied PPG DP43LF epoxy primer to the parts. I just thought if there is something that would aid me in the rusty areas that would be great.This is my first time and I want to do it right.

I think MartinSr answered in this post on the same subject: http://www.chevelles.com/forum/Forum3/HTML/004130.html

Jimmy, I will "chime in" only to say that you are right on the money.
READ THE TECH SHEETS, and use every product the way it was intended. I know guys who scuff sand a car with Comet, and don't seem to have a problem, but WHY? Why would you want to do that when there are scuff gels on the market that the manufacture spent more money than you and I make in a few years to develope. Don't try to save money with "home brews". http://www.chevelles.com/forum/smile.gif
As far as product recommendations, nothing is better than the store you are going to buy the rest of the system. Find your system, I can tell you right now, Dupont, PPG, S-W/M-S, ect. are VERY similar in technology and any will give you first class results. The trick is to have a store that will support you in all your needs and questions. This is the most important thing in choosing.

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1965 Buick Gran Sport Convertible
1965 Buick Skylark H/T
"Fan of most anything that moves human beings"