NO NO NO NO!! That's never a good idea.
You cannot put private loans into the federal program, you can only put your federal loans into a private program raising your low federal interest rates up to the higher private rates - usually at least 10%. You also lose any federal benefits such as deferal and forbearance or any chance at loan forgiveness.
You can consolidate them separately but there are often few advantages to consolidating your private loans. I believe Citibank is the only one offering to fix the rates, with everyone else they are still variable so you don't really save anything. It can't hurt to call around and see what you can find though. Try My Rich Uncle, they seem to be a decent, student-oriented company. Of course one of the things I liked about them is they gave discounts for academic achievement and the government, in their infinite wisdom, has just outlawed that. I don't know what they are offering now as incentives but I'm sure they came up with something else.