The law attempts to delineate between that which is ok, from that which is punishably bad.
OK to shake someone's hand. Not OK to kill someone.
OK to donate (legal amounts of) money to a campaign fund. Not OK to buy a congressman a house.
OK for a congressman to think good thoughts about contributers at voting time, and to vote any way they want. Not OK to introduce special clauses into bills that benefit no one but said contributers.
There seems to be clear evidence of fraud on Abramoff's part. They seem to be cutting a deal with him. That makes it seem like he can testify against bigger fish than himself. That's just the way it usually works. We will see how it pans out.
Whatever deal he cuts will not protect him from the civil court cases that - I guarantee you - will follow.