Simultaneous Entry Of Records

Hi,
I am facing an issue as described in the following:

Scenario:
I have an assignment where the client requires to store its customer detail electronically (ie In soft copy). (e.g Last 5 years data are in hard copy/hard Form format).

They require an application that will help them to enter 10,00,000 records (customer details) in a given span of time.

They have suggested that almost 70-80 operators will work simultaneously in respective console to enter customer information.

Now, every active customer has account number. New customers are given account number from inactive ones.

So, there is a high possibility that while operator1 enters new customer detail and at the same time operator2 while attempting to enter the old customer detail of the same account number will not be allowed as the account number is unique.

My concern is:
With such a huge number of records to enter, will the application get slow. I plan to develop it in access_FrontEnd and SQLserver2000_BackEnd.

I wish to validate account number search: ie when operatorX attempts to add customer record to database it will first check if the same account number already exists.

If I am able to make anyone understand my concern.

Any suggestion is highly appreciated.
Any suggestion in the design aspect…

Thanks,
Prodigy.