@tmd63
I disagree. You need to change the structure at the time of import.
If you maintain these 600+ fields in three or more separate tables, the time taken to do the import will be vastly outweighed by the time you will spend battling Access to write queries, create forms, reports etc as you will be trying to force Access to behave like a spreadsheet rather than use it the way its designed to be used.
As previously stated, spend time now designing properly normalised tables. Then link to your CSV file(s) and run a series of append queries or a custom procedure to import the data into those tables.
Do it properly now and you won't regret it. Carry on as planned and you definitely will.
Good luck