OscMax (oscommerce) customer database issue

I had someone install oscmax 2.0 and transfer my previous oscommerce customers to the new customer database. However the customer ID's did not pick up where the old ones left off, it started back at 1. So now the "new customer #1" can see "old customer #1" private information if they click on My Account or Order History. I need to keep the old customers, of which I had about 300, and start my new costumers with ID's starting at #301 Bidder, please let me know how you will do this, if it will be done manually or if its going to be a simple transfer of the old database and how long it will take. I just need it to be done, and done correctly this time, I have already wasted money. But more importantly it needs to be done urgently so that my customers' privacy will not be invaded.