I need to know about Provanta Corporation, based in San Jose,
California.  Are they a legitimate company?  I have done some research
on this company, but I need to know what is their track record for
succesfully negotiating debts for people.  Good-bad-or whatever you
find would be appreciated.

I can qualify myself this way .....I work in debt collections.

Simply put why have somebody negotiate for you when you can do it
yourself. Are you afraid of talking to your creditors. For the most
part the creditors will not do settlements lower then 30 percent off
the full balance of the bill.
You can get some to got down to 90 percent off but those will fall off
your credit reports soon if they are willing to go that low.
You will be responsible to pay taxes on the difference if you save a
lot of money.
This will also reflect on your credit report that you settled.
Simply put it is not a great program for most. 
I do know there is a Lot of article about companys like these in
consumer reports and other mags.